Machine Design - Prof. Ibrahim Shaikh Answers To Questions 2015 Machine Design [email protected] Mob.: 9892128099 . 2

Short Answers To Questions 2015

Machine Design

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Machine Design


Preface

This book, Machine Design-Short Answers to Question, is intended for use at the

undergraduate level in Mechanical or Automobile engineering curriculum. This book is compiled with the aim of providing the theory questions and their short answer at one point and to enable the students to prepare for viva voce and other engineering exams. The book is arranged in simple question-answers format, covering all the topics of machine design subject in mechanical engineering. Suggestion and comments for the improvement of the book will be appreciated.

Prof. SHAIKH IBRAHIM ISMAIL

Automobile Engineering Department

M.H.Saboo Siddik College Of Engineering

Mumbai



Machine Design


Acknowledgments For this book, information has been obtained from various sources such as books, catalogues, journals and internet through students of AUTOMOBILE ENGINERING department (T.E.-2011-2012) who contributed the answers to the questions given to them. I extend my thanks to my student NISHITH UNNIKRISHNAN who designed the cover page of this book. Also, I extend my thanks to HUZEFA CHATRIWALA who took the pain to format the contents of the book . Finally, I would like to acknowledge the encouragement received from my teacher and guide Dr.G.T.Thampi, Principal Thadomal Shahani College of Engineering, Mumbai.

Prof. SHAIKH IBRAHIM ISMAIL

Automobile Engineering Department

M.H.Saboo Siddik College Of Engineering

Mumbai



Machine Design


Table of Contents

Ch.1- Fundamentals of Machine Design ..................................................................................................... 5

Ch.2- Engineering Materials ...................................................................................................................... 13

Ch.3- Manufacturing Consideration In Design .......................................................................................... 35

Ch.4- Design against Static Load ............................................................................................................... 48

Ch.5 - Fundamentals of Machine Design .................................................................................................. 61

Ch.6- power screws ................................................................................................................................... 65

Ch.7- Design of Bolted Joint ...................................................................................................................... 75

Ch.8- Design of Welded Joint .................................................................................................................... 80

Ch.9- Design of Shaft ................................................................................................................................. 87

Ch.10- Design of Springs ........................................................................................................................... 98

Ch.11 – Design of Clutch ......................................................................................................................... 107

Ch.12 – Design of Brake .......................................................................................................................... 115

Ch.13 – Design of Belt Drives .................................................................................................................. 121

Ch.14- Fundamentals of Machine Design ............................................................................................... 133

Ch.15- Selection of Bearings ................................................................................................................... 144

Ch.16- Design of Gears ............................................................................................................................ 159

Ch.18- Design of Helical Gears ................................................................................................................ 172

Ch.19- Design of Worm Gears ................................................................................................................. 177

Ch.22- Design of Thin Cylinder ................................................................................................................ 181



Machine Design


Ch.1- Fundamentals of Machine Design

1.1) Define machine design.

Ans) Machine design is defined as the use of scientific principles, technical information and imagination in the description of machine to perform the specific function with maximum economy and efficiency.

1.2) What is the final outcome of machine design process?

Ans) Prepare assembly, Detail drawing and Modify drawing after testing prototype model are the final outcome of the machine design process.

1.3) What are the steps in the machine design process?

Ans) Market survey, Define specification of product, select proper mechanism, prepare general layout and select joining method, Design individual components and finally prepare assembly and detail drawings and modify drawing after testing prototype model.

1.4) Name the various requirements of product giving suitable example.

Ans) Requirements of products include the output capacity of the machine, service life, cost and reliability. In some cases the overall dimension and weight of the product are specified.

For example; While designing a scooter:: (i) Fuel consumption = 40km/l (ii) Max speed = 85km/hr (iii) width=700mm, length=1750mm, height=100mm, weight=90kg (iv) Cost = 15000 to 18000 Rs.

1.5) How will you select a mechanism for a product?

Ans) Depending upon the cost-competitiveness, availability of raw material and manufacturing facility is the best way to select the mechanism for the product.

1.6) Prepare a block diagram showing the general layout of EOT and give names of each assembly.

Ans) Electrically operated Overheated Traveling (EOT) consist of following components.



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(i)electric motor for power supply

(ii) flexible coupling to connect the motor shaft to the clutch shaft

(iii) clutch to connect or disconnect the motor

(iv) gear box to reduce the speed from 1440- 15 rpm

(v) rope drum, to convert the rotary motion of shaft to the linear motion of wire rope

(vi) break to stop the motion.

1.7) What type of information is given on the final drawing of product?

Ans) Material of the component, dimensions, tolerances, surface finish grades and machining symbols are specified on the final drawing of product.

1.8) What are the basic requirements of machine element?

Ans) Strength, Rigidity, Wear resistance, Minimum dimension and weight, Manufacturability, Safety, Conformance to standards, Reliability, Maintainability and Minimum life cycle cost are the basic requirements of machine elements.

1.9) What are the steps involved in the design of machine element?

Ans) Specify function of element, Determine forces acting on element, Select suitable material for element, Determine failure mode of element, Determine geometric dimension of element, modify dimension for assembly and prepare working drawing of element are the steps in the design of machine element.

1.10) What is design by Craft evolution?

Ans) Design by Craft evolution has following features.

The craftsman does not prepare dimensional drawing for their products these products are developed by trial and error method. The complete manufacturing of product can be subdivided into separate pieces, which can be made by different people, much of the intellectual activity is taken away from the shop floor and assigned to the design engineers.

1.11) Name the products produced by craft evolution?

Ans) Bullock cart, rowing boat, plow and musical instruments are some of the products which are produced by craft evolution.



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1.12) What are the steps in the ‘Design by craft evolution’ ?

Ans) The steps are as follows,

1.13) Why has ‘Design by craft evolution’ become obsolete?

Ans) Craft evolution method has become obsolete due to two reason.

(i) This method cannot adapt to sudden change in requirement.

(ii) The product cannot be manufacture on mass scale.

1.14) What is ‘Design by drawing’ method?

Ans) Design by drawing method can be understood by the following points,

(i) Dimensions of the product are specified in advanced of their manufacture.

(ii) The complete manufacturing of the product can be subdivided into separate pieces.

(iii) when the product is to be developed by trial and error method, the process is carried out on a drawing board instead of shop floor.

iv) Much of the intellectual activity is taken away from the shop floor and assigned to the design engineers.

1.15) What are the advantages of ‘design by drawing method’ over ‘design by craft evolution’?

Ans) (i) Dimensions of the product are specified in advanced of their manufacture . (ii) The complete manufacturing of the product can be subdivided into separate pieces, which can be made by different people. (iii) In this method, no trial and error method. Hence this method is cheaper than the craft by evolution method.

1.16) Define design synthesis.

Ans) The design synthesis is defined as the process of creating or selecting configurations, materials, shapes and dimensions for a product.

1.17) Distinguish between design synthesis and design analysis.

Ans) In design analysis the designer assumes a particle mechanism ,particular material and mode of failure for the component however design synthesis does not permit such assumption, here designer selects the optimum configuration from a no. of alternative solution.



Machine Design


1.18) What is standardization?

Ans) Standardization is defined as obligatory norms, to which various characteristics of a product should conform. The characteristics include materials, dimensions and shape of components, method of testing and method of marking, packing and storing of the product.

1.19) Give example of Indian Standards for engineering materials.

Ans) I.S. 210 : Specifies seven grades of gray cast iron designated as FG150, FG200, FG220, FG260, FG300, FG 350 and FG400. The number indicates ultimate tensile strength in N/mm2

I.S. 1570(Part 4): Specifies chemical composition of various grades of alloy steels. For example alloy steel designated by 55Cr3 has 0.5-0.6% carbon, 0.10-0.35% silicon, 0.6-0.8% manganese and 0.6-0.8% chromium.

1.20) Give example of Indian Standards for dimension of machine element.

Ans) I.S. 2494 : Specifies dimensions and shape of the cross section of v-belt for power transmission.

I.S. 5129(Part 1) : These dimension includes inner and outer diameter of oil seal units.

1.21) Give examples of Indian standards for fits and tolerances.

Ans) Standards for fits are illustrated in I.S.2709 & for tolerances in I.S.919.

1.22) Give examples of Indian standards for testing of machine elements.

Ans) I.S.2825 is for testing of pressure vessels.

1.23) Give examples of Indian standards for engineering drawings.

Ans) Special publication SP 46 is on engineering drawing practice for schools and colleges.

1.24) What are the three basic types of standards used in design office?

Ans) Company standards, national standards (BIS, BS, AISI), international standards (ISO)

1.25) What are the advantages of standardization?



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Ans) Interchangeability, reduced time & effort to design, improve quality & reliability of the design.

1.26) What do you understand by size of the product? Give examples.

Ans) Size is a general term including load carrying capacity, power transmitting capacity, speed, dimensions etc.

1.27) What are the preferred numbers?

Ans) Preferred numbers are used to specify the sizes of the products.

1.28) How many basic series are used? How will u denote them?

Ans) There are five basic series viz. R5, R10, R20, R40, R80.

1.29) What is R5 series? Develop R5 series from 1 to 10.

Ans) R5 series increase is of 58%. 1, 1.6, 2.5, 4, 6.3, 10.


Ans) In R10 series increase is of 26%. 1, 1.25, 1.6, 2, 2.5, 3.15, 4, 5, 6.3, 8, 10.


Ans) In R20 series increase is of 12%. 1, 1.12, 1.25, 1.4, 1.6, 1.8, 2, 2.24, 2.5, 2.8, 3.15, 3.55, 4, 4.5, 5, 5.6, 6.3, 7.1, 8, 9, 10.


Ans) In R40 series increase is of 6%. 1,1.06,1.12,1.18,1.25,1.32,1.4,1.5,1.6,1.7,1.8,1.9,2,2.12,2.24,2.36,2.5,2.65,2.8,3,315,3.35,3.55,3.75,4,4.25,4.5,4.75,5,5.3,5.6,6,6.3,6.7,7.1,7.5,8,8.5,9,9.5,10.

1.33) What is derived series?

Ans) Series formed on the basis of basic series are derived series.

1.34) How will you form derived series?

Ans) By reducing or increasing the numbers of a basic series.



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1.35) What is R 10/3 (…..,8 ,…..) designation of derived series?

Ans) This series compromises of every 3rd term of R10 series unlimited at both ends having number 8 in the series.

1.36) What is R 20/4 (1,…....,1000) designation of derived series?

Ans) This series compromises of every 4th term of series R20 from 1 to 1000.

1.37) What is R 20/3 (200,…..) designation of derived series?

Ans) This series compromises of every 3rd term of series R20 having lower limit 200 & no higher limit.

1.38) What is R 20/3 (…....200) designation of derived series?

Ans) This series compromises of every 3rd term of series R20 having higher limit 200 & no lower limit.

1.39) What is an industrial design?

Ans) Industrial design is the one which is aesthetically pleasing.

1.40) What are the five basic forms for the shape of the product?

Ans) Step, stream, taper, shear, sculpture.

1.41) What is the relationship between functional requirement and external appearance of product?

Ans) Functional requirements result in shapes which are aesthetically pleasing.

1.42) Explain the meaning of different color as per Morgan code.

Ans) Morgan has suggested the meaning of colors

red-Danger,Hazard,Hot

orange-possible danger

yellow-caution

green-safety

blue-caution, cold



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grey-dull

1.43) Define ergonomics.

Ans) Ergonomics is the scientific discipline concerned with the understanding of interactions among humans and other elements of a system, and the profession that applies theory, principles, data and methods to design in order to optimize human well-being and overall system performance.

1.44) What is the scope of ergonomics in product design?

Ans) Ergonomics has a wide scope in product designing it increases profitability, reduces injuries and enhances the employee’s work-life quality.

1.45) Explain man-machine joint system.

Ans) Human–machine system is a system in which the functions of a human operator (or a group of operators) and a machine are integrated. This term can also be used to emphasize the view of such a system as a single entity that interacts with external environment.

1.46) What are the types of controls?

Ans) following are the types of controls :-1)lever. 2)cranks 3)Hand wheels.

1.47) What are the ergonomic considerations in design of controls?

Ans) Following are the considerations

1)the shape of a control component which comes in contact with hands should be in conformity with anatomy of human hands.

2)proper color produces beneficial physiological effects, the control should be painted red with grey background.

1.48) What are the types of displays?

Ans) The visual displays are classified as:

1)displays giving quantitative measurement like speedometer, voltmeter.

2)displays giving state of affair like the red lamp indicator

3)displays indicating predetermined settings.



Machine Design


1.49) What are the ergonomic considerations in design of displays?

Ans) Following are the considerations:

1)the number of sub divisions between numbered divisions should be minimum.

2)the pointer should have a knife edge with a mirror in the dial to minimize parallax error.

1.50) What is concurrent engineering?

Ans) Concurrent engineering is a work methodology based on the parallelization of tasks (i.e. performing tasks concurrently). It refers to an approach used in product development in which functions of design engineering, manufacturing engineering and other functions are integrated to reduce the elapsed time required to bring a new product to the market.

1.51) Distinguish between sequential design and concurrent engineering.

Ans) Sequential design is a linear method of production in which production takes place in n-number of steps one after another.

While concurrent engineering is the method in which different steps of production are carried out at the same time.

Sequential design is a slower approach.

While concurrent engineering is a faster approach and saves time.



Machine Design


Ch.2- Engineering Materials

2.1) What is cast iron?

Ans) Cast iron is a mixture of iron, carbon and steel derived from pig iron usually referred to as gray iron.

2.2) What is the percentage of carbon in cast iron and steel?

Ans) Steel has 0.3 to 2 % carbon content, while cast iron has 2.1 to 4% carbon by weight.

2.3) What are the advantages of cast iron form design considerations?

Ans) Advantages of cast iron form design considerations are:

Cast iron components can be given any complex shape without involving costly machining operations.

It has more resistance to wear even under the conditions of boundary lubrication.

2.4) What are the disadvantages of cast iron form design considerations?

Ans) Disadvantages are:

Even with the same composition , the tensile strength of a cast iron part decreases as the thickness of the section increases

2.5) Why does the tensile strength of cast iron decreases as the thickness of part increases?

Ans) As the thickness increases the carbon content increases ,thus the tensile strength decreases.

2.6) How will you classify cast irons?

Ans) Cast irons are classified on the basis of the carbon content in their microstructure as

(a)grey cast iron

(b)malleable cast iron

(c)ductile cast iron.



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2.7) What is grey cast iron?

Ans) Gray cast iron also known as flake graphite cast iron is a type of a casting iron in which most of the carbon is present as graphite flakes.

2.8) How will you designate grey cast iron?

Ans) Grey cast iron is specified by the symbol FG followed by the tensile strength in N/mm2.i.e GF200.

2.9) What is FG200 designation of cast iron?

Ans) FG200 is a Grey cast iron with an ultimate tensile strength of 200 N/mm2.

2.10) How will you designate grey cast iron with minimum tensile strength of 300 N/mm2

Ans) FG300 is the designation of grey cast iron with minimum strength of 300 N/mm2

2.11) Name the components made of grey cast iron

Ans) The components such as cylinder block , brake drum, clutch plate, cylinder and cylinder head, gears and housing of gear box, flywheel and machine frame, bed and guide.

2.12) What are white cast iron

Ans) White cast iron are formed when most of the carbon content in the alloy forms iron carbide and there are no graphite flakes.

2.13) How will you designate white cast iron

Ans) It can be designated in three forms blackheart, pearlitic, and whiteheart in symbol BM, PM, WM followed by minimum tensile strength in N/mm2.

2.14) What are BM350 and PM600 designation of cast iron

Ans) BM350 is blackheart malleable cast iron with minimum tensile strength of 350 N/mm2.PM600 is pearlitic malleable cast iron with minimum tensile strength of 600N/mm2.

2.15) How will you designate blackheart malleable cast iron with minimum tensile strength of 350 N/mm2



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Ans) BM350 is the designation of blackheart malleable cast iron with minimum tensile strength of 350 N/mm2.

2.16) How will you designate whiteheart malleable cast iron with minimum tensile strength of 400 N/mm2

Ans) WM400 is the designation of whiteheart malleable cast iron with minimum tensile strength of 400 N/mm2.

2.17) How will you designate pearlitic malleable cast iron with minimum tensile strength of 600 N/mm2

Ans) PM600 is the designation of pearlitic malleable cast iron with minimum tensile strength of 600 N/mm2.

2.18) How will you designate spheroidal graphite cast iron with minimum tensile strength of 900 N/mm2 and elongation of 2%

Ans) SG800/2 is the designation of spheroidal graphite cast iron with minimum tensile strength of 800 N/mm2 and minimum elongation of 2%.

2.19) Name the components made of white cast iron

Ans) Thin castings, pipe fittings, switch gear equipments, fitting for bicycle and motorcycle frames, iron castings etc.

2.20) What is spheroidal graphite cast iron

Ans) Spheroidal cast iron are also called as ductile or nodular cast iron as carbon is present in the form of spherical nodules called spherulites or globules.

2.21) How will you designate spheroidal cast iron

Ans) SG200 is the designation of spheroidal cast iron with minimum tensile strength of 200 N/mm2.

2.22) What is SG200/2 designation cast iron

Ans) It is spheroidal cast iron with minimum tensile strength of 200N/mm2 and minimum elongation of 2%.

2.23) Name the components made up of spheroidal graphite cast iron



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Ans) It is dimensionally stable at higher temperatures hence use to manufacture furnace doors and components, pipelines in chemical and petroleum industries.

2.24) How will you designate steel on the basis of tensile strength

Ans) For high strength and high elongation 65C6 and for low strength and high elongation 7C4.

2.25) What are Fe 360 and FeE 250 designation of steel

Ans) Fe 360 indicates a steel with minimum tensile strength of 360 N/mm2 and FeE 250 indicates a steel with minimum yield strength of 250 N/mm2.

2.26) How will designate plain carbon steels

Ans) A figure indicating 100 times the average percentage of carbon ,a letter C and a figure indicating 10 times the average percentage of manganese.

2.27) What is 55C4 designation of steel

Ans) 55C4 is the plain carbon steel with 0.55% carbon and 0.4% manganese.

2.28) How will you designate plain carbon steel with minimum tensile strength of 320N/mm2

Ans) 7C4 is the designation of the plain carbon with minimum tensile strength of 320 N/mm2.

2.29) How will you designate plain carbon steel with minimum yield strength of 320 N/mm2

Ans) 40C8 is the designation of plain carbon steel with minimum yield strength of 320 N/mm2. Since minimum yield strength is 55% of minimum tensile strength(580).

2.30) How will you designate plain carbon steel with 0.4 carbon and 0.8 manganese?

Ans) 40C8

2.31) How will you designate free cutting steel?

Ans) A figure indicating 100 times the average percentage of carbon.

A letter C



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A figure indicating 10 times the average percentage of manganese.

A symbol ‘S’ ‘Se’ ‘Te’ or ‘Pb’ depending upon the element that is present and which makes the steel free cutting.

A figure indicating 100 times the average percentage of the above element that makes the the steel free cutting.

e.g.; 25C12S14

0.25%-Carbon

1.2%-Manganese

0.14%-Sulphur

2.32) What is 25C12S12 designation of steel?

Ans) 0.25%-Carbon

1.2%-Manganese

0.12%-Sulphur

2.33) What is 15Cr3 designation of steel?

Ans) 0.15%-Carbon

0.75%-Chromium

2.34) What is 16Ni3Cr2 designation of steel?

Ans) 0.16%-Carbon

0.8%-Nickel

0.6%-Chromium

2.35) What is high alloy steel?

Ans) Stainless and heat-resisting steels are called high alloy steel.

2.36) How will you designation high alloy steels?

Ans) A letter ‘x’

A figure indicating 100 times the average percentage of Carbon.

Chemical symbol for alloying element each followed by the figure for its average percentage content rounded off to nearest integer.



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Chemical symbol to indicate specially added element to attain desired properties.

e.g.; X15Cr25Ni12

0.15%-Carbon

25%-Chromium

12%-Nickel

2.37) What is X20Cr18Ni2 designation of steel?

Ans) 0.20%-Carbon

18%-Chromium

2%-Nickel

2.38) What is low Carbon steel?

Ans) Low Carbon steel contains less than 0.3% of carbon. Its popular as Mild-steel. Low carbon steel are soft and very ductile. They can be machined and welded easily.

2.39) What is medium carbon steel?

Ans) Medium carbon steel has carbon content in the range of 0.3% to 0.5%.

2.40) What is high carbon steel?

Ans) High carbon steel contains more than 0.5% of carbon. They are called hard steel or tool steels.

2.41) What is mild-steel?

Ans) Low Carbon steel contains less than 0.3% of carbon. Its popular as Mild-steel.

2.42) What is the percentage of carbon in mild-steel?

Ans) 0.3% of carbon.

2.43) What are important components made of plain carbon steel?

Ans) 7C4) automobile bodies and hoods

10C4) cam and cam shaft, worm, gudgeon pin.



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30C8) socket, tie rod, yoke, lever rocker arm.

40C8) transmission shaft, crank shaft, spindle, connecting rod, stud and bolt.

50C4) worm, gear and cylinder.

2.44) What is the effect of addition of sulphur in carbon steels?

Ans) The machinability of these steel is improved due to addition of sulphur.

2.45) What are the advantages of plain carbon steel?

Ans) High ductility

Welded easily

Low cost

2.46) What are the disadvantages of plain carbon steel?

Ans) Very poor heat conductor

Reacts to foods

Rusts easily

2.47) Define alloy steel?

Ans) Alloy steel is define as carbon steel to which one or more alloying elements are added to obtain certain beneficial effect.

2.48) Name the various alloying elements in alloy steel?

Ans) Silicon

Manganese

Nickel

Chromium

Molybdenum

Tungsten

2.49) What are advantages of alloy steel?

Ans) Higher strength, hardness and toughness



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High values of hardness and strength can be achieved for component with larger section thickness

Higher hardenability

Alloy steels retain their strength and hardness at elevated temperature

Alloy steels have high resistance to corrosion and oxidation

2.50) How will you designate alloy steel with following composition?

Carbon=0.35%-0.45%

Chromium=0.90%-1.1%

Ans) 40Cr4

2.51) How will you design it alloy steel with following composition

Ans) Carbon =0.12 to 0.20%

Nickel=0.80 to 1.2%

Chromium=0.60 to 1%

A 16NI10cr8

16 is the average percentage of carbon,10 is the average percentage of nickel and 8 is average percentage of chromium

2.52) What is the effect of addition of silicon on alloy steel

Ans) A silicon increases strength and hardness without lowering ductility

2.53) What is the effect of addition of manganese in alloy steel

Ans) Manganese increases hardness and strength .it also increases depth of hardening.

2.54) What is the addition of nickel in alloy steel

Ans) Nickel increases strength and hardness and toughness without sacrificing ductility. it increases hardenability and impact resistance at low temperature.

2.55) What is the effect of addition of chromium in alloy steel

Ans) Chromium increases hardness and wear resistance and also retains strength and hardness at elevated temperature



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2.56) What is the effect of addition of molybdenum in alloy steel

Ans) Molybdenum increases hardness and wear resistance. it resists softening of steel during tempering and heating

2.57) What are the important component made of alloy steel

Ans) The following are the components made of alloy steel

Spring wires,screws,bolts and axles, gears etc

2.58) What is the ASTM class no 20 designation of cast iron

Ans) This class no gives minimum tensile strength in kpsi

Hence ASTM class no 20 has minimum ultimate tensile strength of 20000 psi

2.59) What is GG -12 designation of cast iron

Ans) GG-12 indicates grey cast iron with minimum ultimate tensile strength of 12 kgf/mm2

2.60) What are the four basic heat treatment processes

Ans) Annealing, normalizing, quenching and tempering

2.61) What is annealing? what is its objective?

Ans) Annealing consist of heating the component to a temperature slightly above the critical temperature followed by slow cooling .

It reduces hardness and increases ductility

2.62) What is normalizing and what is its objective?

Ans) Normalizing is similar to annealing except that the component is slowly cooled in air.

It is used to remove the effects of the previous heat treatment processes

2.63) What is quenching and what is its objective?

Ans) Quenching consist of heating the component to a critical temperature and cooling it rapidly in water or air.



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It increases hardness and wear resistance.

2.64) What is the tempering and what is its objective?

Ans) Tempering consist of reheating the quench component to a temperature below the transformation range followed by cooling at desire rate.

It restores the ductility and reduces brittleness due to quenching.

2.65) What is case hardening ? how it is achieved?

Ans) The stress distribution is not uniform across the cross section of the component and the surface is heavily stress than core which can be removed by case hardening.

It is achieved by two ways

1) by altering the structure at the surface by local hardening

2) by altering the structure as well as the composition at the surface

2.66) What is flame hardening? where do you recommend?

Ans) Flame hardening consist of heating the surface above the transformation range by means of flame followed by quenching

It is recommended under the following condition

1) where the component is large

2) where a small area of the workpiece is to be hardened

3) where dimensional accuracy is desirable

2.67) What is induction hardening and where do you recommend?

Ans) Induction hardening consist of the heating the surface by induction in the field of an alternating current .induction hardening produces case depth as small as 0.1mm hence it is used to produce minimum case depth.

2.68) What is case carburizing where do you recommend it?

Ans) Case carburizing consist of introducing carbon at the surface layer by heating from 882 to 980 c.

It is recommended for case depth upto 2 mm

2.69) What is carbonitriding and where do you recommend it?



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Ans) Carbonitriding consist of introducing carbon and nitrogen simultaneously at a surface layer by heating from 650 to 920 c in the atmosphere of anhydrous ammonia then quench in a suitable medium. medium carbon steels are carbonitrided upto 0.6mm

The process gives higher wear resistance compare to case carburizing.

2.70) What is nitriding ?where do you recommend it?

Ans) Nitriding consist of exposing the component to the action of nascent nitrogen in a gases or liquid medium from 490 to 590 c .

The surface produce consist of nitrides followed by tougher diffusion zone case depth upto 0.1mm are obtained. Nitrided components are use for application requiring high resistance to abrasion, high endurance limit and freedom from distortion

2.71) Compare Cast iron and cast steel component.

Ans) Cast steels usually contain less than 1% carbon while cast iron normally contains 2% to 4% carbon.

2.72) Compare steel and cast steel component.

Ans) Cast steel can be molded and also it is lighter in weight.

2.73) How will you designate Carbon steel castings?

Ans) A Carbon steel casting of yield stress ultimate tensile strength of 280 and 520 N/mm2 respectively, will be designated as a carbon steel casting of grade 280)520.

2.74) What is grade 200)400 designation of carbon steel castings?

Ans) Designation of grade 200)400 is carbon steel casting of grade 200)400 have yield stress of 200 N/mm2 and an ultimate tensile strength of 400 N/mm2.

2.75) Name the components made of Carbon steel castings.

Ans) Tools used in lathe machines.

2.76) How will you designate high tensile steel castings?



Machine Design


Ans) A high tensile steel castings with minimum ultimate tensile strength of 1030 N/mm2 is designated as CS1030.

2.77) What is CS640 designation of high tensile steel castings?

Ans) CS640 is a steel casting with minimum ultimate tensile strength of 640 N/mm2.

2.78) Name the components made of high tensile steel castings.

Ans) knuckle joint in agricultural machinery and transportation equipments.

2.79) How will you designate carbon steel casting with ultimate tensile strength of 400N/mm2 and yield stress of 200 N/mm2?

Ans) Carbon steel casting with tensile strength of 400 N/mm2 and yield stress of 200 N/mm2 will be designated as “Carbon” steel casting of grade 200)400”.

2.80) How will you designate high tensile steel casting with ultimate tensile strength of 1030 N/mm2 ?

Ans) Designation of high tensile steel casting with ultimate tensile strength of 1030 N/mm2 will be CS 1030.

2.81) What are the advantages of aluminum alloy for mechanical components ?

Ans) Major advantage of aluminum alloy is that it provides low specific gravity . Also with this it provides ease of fabrication, corrosion resistance and high thermal conductivity.

2.82) How will you designate aluminum alloy castings?

Ans) Cast aluminum alloys are specified by a ‘four digit system’ . First digit identifies major alloying elements where second digit identifies average percentage of major element where third and fourth digit identifies minor alloying element.

2.83) What is 2585 designation of aluminum alloy castings?

Ans) Complete designation of 2585 is such that, aluminum alloy casting consists of 9.8% Cu,1.0% Fe and 0.25% Mg.

2.84) Name the components made of aluminum alloy castings.



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Ans) Alloy 4450:Engine cylinder blocks , Alloy 2280:connecting rods , Alloy 2250:pistons and cylinder heads.

2.85) How will you designate wrought aluminum alloy?

Ans) Wrought aluminum alloy are specified by ‘five digit system’ . Where first digit identifies major alloying elements, second digit identifies average percentage of major elements where third , fourth , fifth digit identifies minor alloying element.

2.86) What is 24345 designation of wrought aluminum alloy?

Ans) First digit – Identification of copper :2 , second digit – 4*2= approximately 8% 0f major alloying element , third digit) Identification of Manganese:3 , Identification of silicon:4,Identification of Magnesium:5.

2.87) Name the components made of wrought aluminum alloy.

Ans) Alloy 24534:Stressed components of aircraft , Alloy 54300:welded structure, Alloy74530:welded pressure vessels.

2.88) What are the advantages of copper alloy form design considerations?

Ans) Copper alloy which is easily available and extractable has major advantage as it does not get rust when exposed to air.

2.89) What are the disadvantages of copper alloys form design consideration?

Ans) Major disadvantage of copper alloy is that , it has no resistance to current also it has high thermal conductivity.

2.90) What are the advantages and disadvantages of brass form design consideration?

Ans) Brass has advantage as it has better machinability and thermal conductivity. ere disadvantage is that, strength and ductility depends upon zinc content. zinc is used for better strength.

2.91) Name the components made of brass.

Ans) Brass are used in manufacture of locks, gears, bearings, doorknobs,

ammunition, and valves, plumbing components, electrical applications and

musical instruments.



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2.92) What are the advantages and disadvantages of phosphor-bronze from

Design considerations??

Ans) ADVANTAGES

They offer resistance towards fatigue

They are resistant to chemical corrosion

Phosphorous increases the wear resistance and stiffness of alloy

Good machinability

Tensile strength from 295-695N/mm

Hardness from 80-240VP

DISADVANTAGES

It is not heat treatable

It cannot withstand high temperatures

2.93) Name the components made of phosphor bronze.

Ans) Phosphor bronze is used in manufacturing spring, bolts, bearings,

bushings, pump impellers, piston rings etc.

2.94) What are the advantages of gun metal from design considerations?

Ans) ADVANTAGES

1) Resistant to corrosion from steam and salt water

2) Tensile strength of 221 to 310 MPa

3) Brinell hardness of 65 to 74.

4) Excellent castability and machinablity

2.95) Name the components made from gun metal

Ans) Steam and hydraulic castings, valves, gears, intricate castings, pipe

fittings and Pumps

2.96) What are the advantages and drawbacks of die casting process

Ans) ADVANTAGES

1) Excellent dimensional accuracy


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2) Smooth cast finish

3) Thinner walls can be cast as compared to sand and permanent mold

casting

4) Reduces or eliminates secondary machining operations

5) High production rates

6) Good tensile strength of components

DISADVANTAGES

1) High capital investment

2) Process is limited to high fluidity metals

3) Component cannot be heat treated or welded after casting

2.97) What are die casting alloys?

Ans) Die casting alloys are alloys that can be die casted. Die casting alloys are

normally non-ferrous and there is a large number available with a wide

range of physical and mechanical properties covering almost every

conceivable application a designer might require. Aluminum And Zinc

alloys are most commonly used followed by magnesium, copper and lead

and tin.

2.98) What are ceramics?

Ans) A ceramic is an inorganic, nonmetallic solid prepared by the action of heat and

subsequent cooling.

2.99) What are the advantages and drawbacks of ceramics??

Ans) ADVANTAGES

High compressive strength and stiffness

Extremely high melting point

High hardness and therefore wear resistance

Chemical inertness

Low weight


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DISADVANTAGES

Weakness in tension

Relatively poor shock resistance

Difficulty to obtain complex shapes with close tolerances

Very brittle

2.100) What are the application of ceramic in engineering industries??

Ans) Ceramics are used in aerospace, catalytic converters, pressure sensors,

thermistors, bricks, cements etc

2.101) What is plastic?

Ans) A synthetic material made from a wide range of organic polymers such as

polyethylene, PVC, nylon, etc., that can be molded into shape while soft

and then set into a rigid or slightly elastic form.

2.102) What is monomer? give its examples

Ans) A is an atom or a small molecule that may bind chemically to other

monomers toform a polymer.

Eg. Isoprene

2.103) What is a polymer? Give its example?

Ans) A polymer is a large molecule composed of repeating structural

units (monomer)

Eg. Polyethylene.

2.104) What are the types of plastic?

Ans) There are two types of plastics:

1) Thermoplastics 2) Thermosetting polymers

2.105) What is thermoplastic? Give its examples.

Ans) Thermoplastics are the plastics that do not undergo chemical change in

their composition when heated and can be molded again and again.

Eg. Polyethylene, polypropylene, polystyrene, polyvinyl chloride


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2.106) What is thermosetting plastic? Give its example.

Ans) Thermosetting plastics are plastics that melt and can take shape only

once; after they have solidified, they stay solid. In the thermosetting

process, a chemical reaction occurs that is irreversible.

Eg. Vulcanized rubber, Bakelite, Duroplast, Melamine resin

2.107) Distinguish between thermoplastic and thermosetting plastic

Ans)

THERMOPLASTIC THERMOSETTING PLASTIC

1) )Thermoplastics are the plastics that do not undergo chemical change in their composition when heated and can be molded again and again

2)thermoplastics have relatively weak forces of attraction between the chains

3)they are soft and flexible

1) Thermosetting plastics are plastics that melt and can take shape only once; after they have solidified, they stay solid. In the thermosetting process, a chemical reaction occurs that is irreversible.

2)Cross linking of the molecules in thermosetting plastic is by strong bonds

3)they are hard and brittle

2.108) What are advantages of plastic?

Ans)

1) They can be easily moulded and have excellent finishing

2) They possess very good strength and toughness.

3) They possess good shock absorption capacity.

4) They have low thermal expansion of co-efficient and possess good thermal and electrical insulating property.

5) Advantages of plastic is very good water resistant and possess good adhesiveness.

6) Plastic is strong, good and cheap to produce.

7) Plastic is a recycling process and it does not decompose.

8) Thermoplastics can be reused and restored over again and again..

9) Plastic is an odorless.


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2.109) What are disadvantages of plastic?

Ans) Disadvantages

Nonrenewable resources.

Embrittlement at low temperature.

Deformation under load.

low heat resistant

Poor ductility.

plastics are combustible

2.110) What are filler, plasticizer, flame retardant and pigment? What is their purpose in p plastic material?

Ans) Filler: Fillers are particles added to material plastics to lower the consumption of more

expensive

binder material or to better some properties of the mixtured material.

Plasticizer: Plasticizers are additives that increases the plasticity or fluidity of material

Flame retardant: Flame retardants are chemicals used in thermosets, textiles and

coatings that inhibit or resist the spread of fire.

Pigment: The pigment is the material that changes the colour of the plastic. It is used to give plastic a desired colour.

2.111) Where do we use Polyamide?

Ans) Polyamide is used for gears, bearing, conveyor rollers and automotive cooling fan.

2.112) Where do we use Polyurethane?

Ans) Polyurethane is used for bearing, gears, gasket and seal.

2.113) What is Teflon? Where do you use it?

Ans) Teflon is thermoplastic material. It has low coefficient of friction and self-lubricating characteristics. It is ideally suitable for self-lubricating bearings.

2.114) What is fibre reinforced plastic (FRP)?

Ans) FRP is a composite material in which the low strength of the polymeric material is increased by means of high strength fibres.

2.115) What are the advantages of fibre reinforced plastics?


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Ans) Fibre reinforced plastics offers following advantages)--

1) It has low specific gravity resulting in the light weight construction.

2) It has high specific strength and modulus of elasticity.

3) It has good resistance to fatigue failure, particularly parallel to the direction of the fibres.

4) It has good resistance to corrosion.

2.116) What are the disadvantages of fibre reinforced plastics?

Ans) Fibre reinforced plastics offers following disadvantages)--

1) A composite material containing fibres in single direction is extremely anisotropic.

2) The design of the components made of fibre reinforced plastics is complex.

3) The manufacturing and the testing of the fibre reinforced components is highly specialized.

2.117) What types of fibre are used in fibre reinforced plastics?

Ans) Fibres used in fibre reinforced plastics are glass fibre and carbon fibre.

2.118) What are the advantages of glass reinforced plastics?

Ans) Glass reinforced plastics has following advantages)--

1) Glass can be easily drawn into fibres from molten state.

2) Glass is cheaper and readily available material.

3) Glass fibre is relatively strong.

4) Glass is chemically inert with respect to plastic matrix materials.

2.119) What are the disadvantages of glass reinforced plastics?

Ans) Glass reinforced plastics offers following disadvantages)--

1) Glass reinforced plastic has poor rigidity and stiffness.

2) Its application is limited up to a temperature of 300`C.

2.120) What are the advantages of carbon reinforced plastics?

Ans) Carbon reinforced plastics has following advantages:-

1) Carbon fibre has maximum strength compared with all other fibre materials.



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2) Carbon fibre retains its strength at elevated temperature.

3) Moisture, acids and solvents at ambient temperature do not affect carbon fibre.

4) Carbon reinforced plastic is relatively cheap.

2.121) What are the disadvantages of carbon reinforced plastics?

Ans) Carbon reinforced plastics has following advantages:-

1) Manufacturing techniques required to produce carbon fibre is relatively complicated.

2.122) Distinguish between natural and synthetic rubbers.

Ans) Natural rubber:-

Natural rubber is obtained from rubber latex, which is a milky liquid obtained from certain tropical trees. It is a low cost elastomer. Different varieties of rubber are obtained by adding carbon, silica and silicates. Vulcanized rubber is obtained by sulphur, which is followed by heating.

Synthetic rubber:-

It has properties similar to those of natural rubber .It can be thermoplastic or thermosetting plastic. It is costlier than natural rubber.

2.123) What are the applications of synthetic rubber?

Ans) Applications of synthetic rubber are:-

1) Chloroprene Conveyor and V belts, brake diaphragms and gaskets.

2) Nitrilie Butadiene (NBR) Bushes for flexible coupling and rubber rollers.

3) Polysulfide (Thiokol) Gaskets, washers and diaphragms.

4) Chlorosulfonyl polyethylene(Hypalon)Tank lining, high temperature conveyor belts, seals and gaskets. 5) Silicone) Seals, gaskets and O-rings.

2.124) What is creep?

Ans) Creep is defined as slow and progressive deformation of the material with time under a constant stress.

2.125) Explain the situations where creep is a serious problem.

Ans) Creep of bolt and pipes is a serious problem in thermal power plants.



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2.126) What is creep strength?

Ans) Creep strength of the material is defined as the maximum stress that the material can withstand for a specified length of time without excessive deformation.

2.127) What is creep rapture strength?

Ans) Creep rupture strength of material is the maximum stress that the material can withstand for a specified length of time without rupture.

2.128) Explain the three stages of creep curve.

Ans) The first stage is called Primary creep is shown by AB on the curve. during this stage, the creep rate i.e. the slope of creep curve from A to B progressively decreases with time.

The second stage called Secondary creep is shown by BC on the curve. During this stage, the creep rate is constant. this stage occupies a major portion of the life of the component designer. Secondary creep. recovery process involving highly mobile dislocations counteract the strain hardening so that the metal continues to elongate at constant rate.

The third stage called tertiary creep is shown by CD on the creep curve. During this stage the creep rate is accelerated due to necking and also due to formation of voids along the grain boundaries.

2.129) What are the factors to be considered for selection of material for a machine component?

Ans) The factors which should be considered while selecting the material for a machine component are)--

1) Availability

2) Cost

3) Mechanical Properties

4 Manufacturing Considerations.

2.130) Explain the principle of weighted point method for selection of material for a machine component.

Ans) It consists of four following steps:-



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1) The first step consists of the study of the given application and preparing a list of the desirable properties of the material for the application.

2) The desirable properties are then assigned values. The approximately range of these properties, such as yield strength, endurance strength, hardness,etc. are specified.

3) The desirable properties are divided into two groups--- Go-no-go parameters and discrimination parameters. The "Go-no-go" parameters are the constraints. As an example, if a material is not available, or if it cannot be fabricated into given shape, it is totally rejected. This is a screening step and only those materials, which meet the essential requirement are allowed further consideration.

4) The discrimination parameters are the properties of material, which can be given quantitative values. The weightage depends upon the importance of that particular property in the given application. As an example, in the case of connection rod, the endurance strength may be given a weighting factor of 5.compared with the cost having a weighting factor of 1.In general, the weighting factor varies from 1 to 5.with 1 for the poorest and 5 for the best.



Machine Design


Ch.3- Manufacturing Consideration In Design

3.1) What is manufacturing?

Ans) Manufacturing can be considered as processing the available material in to useful component. E.g. converting mild steel sheet in to car body.

3.2) What are the three categories of manufacturing process? Give their examples.

Ans) 1) Casting process: Housing of gear box

2) Deformation process: Connecting rod, crank shaft.

3) Material removal or cutting process: Transmission shaft, key, bolts, & nuts.

3.3) What is casting process? Give example of component made by casting?

Ans) In casting process molten metals such as cast iron, copper, aluminum, or non metal like plastic are poured in to the mould and solidified in to the desired shape e.g. housing of gear box, flywheel with rim and spokes machine tool beds and guides.

3.4) What is deformation process? Give example of component made by deformation process?

Ans) In deformation process a metal, either hot or cold is plastically deformed in to the desired shape. Forging, rolling, extrusion press workings are the example of component made by deformation process. The product are include connecting rods, crank shaft, I- section beam, car bodies and spring.

3.5) What is cutting process? Give example of component made by cutting process?

Ans) In cutting process the material is removing by means of Using cutting tool. Turning,milling, drilling, shaping, planning, grinding, shaving, and lapping are the example of material removal process. The product induces transmission shaft, keys, bolts and nuts.

3.6) What are the factors to be considered while selecting optimum manufacturing

method for a component?

Ans) 1) Material of component.

2) Cost of manufacture.



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3) Geometric shape of component.

4) Surface finish and tolerance required.

5) Volume of production.

3.7) Name various casting process.

Ans) 1) Sand casting process.

2) Shell- mould casting.

3) Permanent - mould casting.

4) Die casting

5) Centrifugal casting.

3.8) What are the advantages of sand casting process?

Ans) 1) the tooling required for casting process is relatively simple and expensive.

2) This is reducing the cost of sand casting process.

3.9) What are the disadvantages of sand casting process?

Ans) 1) It not possible to achieve close tolerance for cast component. Therefore cast

component required additional machining and finishing, which increase cost.

2) Cast component have a rough surface finishing.

3.10) What is forging?

Ans) In forging the metal in the plastic stage rather than in molten stage is forced to flow in to in to the desired shape.(deformation process)

3.11) Name various forging process.

Ans) 1) Hand forging.

2) Drop forging.

3) Press forging.

3.12) What are the advantages of forging process?

Ans) 1) In forging process, there is relatively good utilization of material compared with machining.



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2) Forged component can be providing with thin selection without reducing the strength this result in light weight construction.

3.13) What are the disadvantages of forging process?

Ans) 1) Forging is a costly manufacturing process

2) forging becomes economical only when parts are manufactured on large scale.

3.14) Name various metal removal process.

Ans) Shaping, Planning, Milling, Drilling, Boring, Reaming, Grinding.

3.15) What are the metal removals processes for machining flat surface?

Ans) For machining flat surface Shaping, Planning, Milling, Grinding, process are used.

3.16) What are the metal removals processes for external cylindrical surface?

Ans) For external cylindrical surface turning on lath, and cylindrical grinding, process are used.

3.17) What are the metal removals processes for internal cylindrical surface?

Ans) For internal cylindrical surface Drilling, Boring, Reaming, and cylindrical grinding, process are used.

3.18) What are the advantages of cutting processes as a manufacturing method?

Ans) 1) Almost any metal can be machined. And it is possible to achieve close tolerance for machine component.

2) Machine component have good surface finishing.

3.19) What are the disadvantages of cutting processes as a manufacturing method?

Ans) 1) Machining process is costly.

2) It not possible to machine thin selection or projection.

3.20) What are the principles of designing cast-iron component?



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Ans) Always keep the stressed area of the part in compression, cast-iron has more compressive strength as compare to tensile strength.

3.21) What are the principal of design for manufacture and assemblies (DFMA)?

Ans) The principle of (DFMA) is to simplify the design, decrease assembly cost, improve product liability and reduce operation time required to bring new product in the market.

3.22) What is tolerance?

Ans)Tolerance is defined as permissible variation in the dimensions of the component.

3.23) What is unilateral and bilateral tolerance?

Ans) Unilateral tolerance: in Unilateral tolerance, the one tolerance is zero, while other take care of all permissible variation in basic size.

Bilateral tolerance: in Bilateral tolerance the variations are given in both the directions from normal size.

3.24) What is fit?

Ans) When two parts are to be assembled , the relationship resulting from difference b/w their sizes before assembly is called a fit.

3.25) What is clearance fit? Give example?

Ans) Clearance fit is a fit which always provides a positive clearance b/w hole and the shaft over entire range of tolerance.

Ex:- door hinges, wheel and axle.

3.26) What is transition fit? Give example?

Ans) Transition fit is a fit which may provide upon the actual values of the individual tolerances of the mating parts. Ex:- pin that needs to go into a slightly smaller hole.

3.27) What is interference fit? Give example?

Ans) Interference fit is a fit which always provides a positive clearance over a whole range of tolerance. Ex:- press fit.



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3.28) What is shaft basis system for giving tolerances?

Ans) In the shaft basis system, the different clearances are obtained by associating various holes with a single shaft, whose upper deviation is zero.

3.29) What is hole basis system for giving tolerances?

Ans) In the shaft basis system, the different clearances and interferences are obtained by associating various shafts with single hole, whose lower deviation is zero.

3.30) What are the advantages of hole basis system over shaft basis system?

Ans) The advantages of hole basis system over shaft basis system is that holes are machined by standard drills, reamers having fixed dimensions, while shafts cannot be machined to fixed dimensions easily and readily.

3.31) What is fundamental deviation?

Ans) The fundamental deviation gives location of tolerance zone w.r.t to zero line.

3.31) How will u designate fundamental deviation?

Ans) The fundamental deviation are designated as follows:

holes to be indicated by capital alphabet, while shafts by small alphabet.

Magnitude of tolerance is indicated by number called grade.

Ex: H7, g6.

3.32) How will u designate magnitude of tolerance?

Ans) Magnitude of tolerance is designated by a number called as grade, as in group of tolerance having some level of accuracy.

3.33) What are the guidelines for selection of clearance fits? Give examples?

Ans) Clearance fits are used when loose running fits which requires adequate clearance.

Ex: lubrication bearings.

3.34) What are the guidelines for selection of transition fits? Give examples?

Ans) Transition fits are used where slight interference is desired.



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Ex: spigot, recess of couplings.

3.35) What are the guidelines for selection of interference fits? Give examples?

Ans) Interference fits are used where considerable gripping is required to have a permanent or semi permanent assemblies.

Ex:- press fits, cotter ins in joints.

3.36) What is selective assembly?

Ans) Selective assembly is a process of sorting the manufactured components into different groups according to their sizes and assembling the components of ane group to another matching group.

3.37) Distinguish between interchangeable and selective assembly?

Ans) Interchangeability allows easy assembly of mating parts. While selective assembly does not.

Complete inspection of components is not required in case of interchangeabilty, while selective assembly does require.

3.38) What are the advantages of selective assembly?

Ans) The advantages of selective assembly is selective assembly is an effective way to achieve precision assembly with economical manufacturing processes based on mass production for mating parts with high precision requirements.

3.39) What are the disadvantages of selective assembly?

Ans) The disadvantages of selective assemblies are as follows:-

complete inspections is required for components.

Interchangeability is effected.

Can only be used for mass productions.

3.40) Explain the symbol of surface roughness?

Ans) Symbol used for surface finish is with its side inclined at 60 degrees to the surface and number indicates surface roughness in microns.



Machine Design


3.41) What are the disadvantages of Hot Working Process?

Ans) It has poor surface finish and results in rapid oxidation of the surface due to high Temperature.

3.42) What is cold working process?

Ans) Metal deformation processes that are carried out below the recrystallization temperature are called cold working process.

3.43) Name various cold working process?

Ans) Cold rolling, cold forging, cold spinning, cold extrusion & cold drawing.

3.44) What are the advantages of cold working process?

Ans) Cold rolled components have better surface finish, high hardness & strength and are more accurate then hot rolled parts.

3.45) What are the disadvantages of cold working process?

Ans) It has poor resistance to shock & vibration and it reduces toughness & ductility.

3.46) What are the principles for design of welded assemblies?

Ans) The main principles are selecting the material with high weld ability, use minimum number of welds, do not shape the parts based on castings or forging, select proper location for welding.

3.47) What is DFM? What is DFMA?



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Ans) DFM stands for design for manufacture & DFMA stands for design for manufacture and assembly & are used to simplify design, decrease assembly cost, and improve product reliability.

3.48) What are the principles of design for manufacture & assemblies (DFMA)?

Ans) The main principles are reducing the parts count, use modular design, optimize part handling & design for part identity.

3.49) Why are fasteners avoided in assemblies?

Ans) Fasteners are difficult to handle and can cause jamming if defective and are major obstacle to efficient assembly and should be avoided wherever possible.

3.50) What is tolerance?

Ans) Tolerance is defined as permissible variation in the dimension of components.

3.51) What are the unilateral and bilateral tolerances?

Ans) a) In unilateral tolerance, one tolerance is zero while other take care of all permissible variation in basic size.

b) In bilateral tolerances, the variations are given in both directions from normal size.

3.52) What is fit?

Ans) When two parts are to be assembled the relationship resulting from the difference between their sizes before assembly is called fit.

3.53) What is clearance fit? Give examples.

Ans) Clearance fit is a fit which always provides a positive clearance between the hole and shaft over the entire range of tolerances. E.g.) hole and shaft system.

3.54) What is transition fit?

Ans) Transition fit is a fit which may provide either a clearance or interference depending upon the actual values of individual tolerances of mating components.

3.55) What is interference fit ?



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Ans) Interference fit is a fit which always provides a positive interference over the whole range of tolerance.

3.56) What is shaft basis system for giving tolerances?

Ans) In this system the size of the shaft is basic size while clearances or interference is applied on the shaft dimension.

3.57) What is hole basis system for giving tolerances?

Ans) In this system the size of the hole is basic size & clearance or interference is applied to shaft dimension

3.58) What are the advantages of hole basis system over shaft basis system?

Ans) Holes are machined by standard drills or reamers having fixed dimension while the shaft can be turned or ground to any given dimension.

3.59) Where do you use shaft basis system?

Ans) Shaft basis system is used in industries using semi finished or finished shafting such as bright bars as raw material.

3.60) Where do you use hole basis system?

Ans) Hole basis system are used widely in the mechanical industries for most of the operations.

3.61) What is fundamental deviation?

Ans) It gives the location of the tolerance zone with respect to the zero line.

3.62) How will u designate fundamental deviation?

Ans) It is indicated by an alphabet, capital letters for holes & small letters for shafts.

3.63) How will u designate magnitude of tolerance?

Ans) It is designated by a number called the grade. There are 18 grades of tolerances with designation IT1, IT2…& IT18.



Machine Design


3.64) Draw a sketch showing fundamental deviation& magnitude of tolerance with respect to zero line.

Ans)

Fundamental Deviation Magnitude of Tolerance

Zero Line

3.65) What do you understand by (50 H8-g7)?

Ans) 50 is the common size for both hole & shaft. H8 - boring – machine reaming. g7 – high precision turning – broaching – honing.

3.66) What are the guidelines for selection of clearance fits? Give examples.

Ans) 1) The fits H7-d8, H8-d9 & H11-d11 are loose running fits. Eg) Plumber block bearings & loose pulleys.

2) The fits H6-e7, H7-e8 & H8-e8 are loose clearance fits. Eg) properly lubricated bearings, requiring appreciable clearances.

3) The fits H6-f6, H7-f7 & H8-f8 are normal running fits. Eg) Shafts of gear boxes, small electric motors & pumps.

4) The fits H6-g5, H7-g6 & H8-g7 are expensive from manufacturing considerations. Eg) precision equipments, pistons slide valves.

3.67) What are the guidelines for selection of transition fits? Give examples.

Ans) The fits H6-j5, H7-j6 & H8-j7 are transition fits. Eg) Spigot & recess of the rigid coupling.

3.68) What are the guidelines for selection of interference fits? Give examples.

Ans) 1) The fits H7-p6 or H7-p7 & H8-f8 are interference fits. Eg) Fitting a brass bush in gear.

2) The fits H6-r5 or H7-r6 is a medium drive fit.

3) The fits H6-s5, H7-s6 & H8-s7 are used for permanent & semi-permanent assemblies of cast iron parts.



Machine Design


3.69) Recommend a suitable class of fit between idler gear & spindle.

Ans) H6-f6.

3.70) Recommend a suitable class of fit between cam shaft & bearing.

Ans) H6-g5.

3.71) Recommend a suitable class of fit between gear shaft & bearing.

Ans) H6-f6.

3.72) Recommend a suitable class of fit between pin & eye in knuckle joint.

Ans) H7-p6.

3.73) Recommend a suitable class of fit between belt pulley & shaft.

Ans) H7-d8.

3.74) Recommend a suitable class of fit between worm wheel & shaft.

Ans) H6-f6.

3.75) Recommend a suitable class of fit between hand wheel& spindle.

Ans) H6-r5.

3.76) Recommend a suitable class of fit between pump impeller & shaft.

Ans) H6-f6.

3.77) Explain the relationship between the grade of tolerance & corresponding manufacturing method.

Ans) The relationship between the grade of tolerance & corresponding manufacturing method is as follows;

Grade 16: sand casting-flame cutting.

Grade 15: stamping.

Grade 14: die casting-moulding.



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Grade 11: drilling-rough turning-boring.

Grade 10: milling-slotting-planning-rolling-extrusion.

Grade 9: horizontal & vertical boring-turning on automatic lathes.

Grade 8: turning, boring & reaming on centre, capstan & turret lathes.

Grade 7: high precision turning-broaching-honing.

Grade 6: grinding-fine honing.

Grade 5: lapping-fine grinding-diamond boring.

Grade 4: lapping.

3.78) What is selective assembly?

Ans) It is the process of sorting the manufactured components into different groups, according to their sizes & then assembling the components of one group to the corresponding components of the matching group.

3.79) Distinguish between interchangeable & selective assemblies.

Ans) Interchangeability is the principle normally employed for the mass production of identical parts within the prescribed limits of sizes. When one component will assemble properly with any mating component, both being chosen at random, then this is interchangeable assembly. Selective assembly is the process of sorting the manufactured components into different groups, according to their sizes & then assembling the components of one group to the corresponding components of the matching group.

3.80) What are the advantages of selective assembly?

Ans) Selective assembly is particularly useful in case of interference fits where a tight control over the range of interference is essential to avoid loosening of mating components.

3.81) What are the disadvantages of selective assembly?

Ans) The disadvantages of this method are:

1] Hundred Percent inspection is required for components with the additional operation of sorting the components.

2] Interchangeability is affected and replacement of worn out parts becomes difficult.

3] The method is useful only for the mass production of the component.



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3.82) What is the effect of surface roughness on performance of machine parts?

Ans) Effects of surface roughness on performance of machine parts are:

1] Friction and wear increases with the increase in surface roughness affecting the performance of the component.

2] It reduces the contact area in the interference fit and there by reduces the holding capacity of the joints.

3] The endurance limit of the component is greatly reduced.

3.83) What are the units of surface roughness measurement?

Ans) The unit of surface roughness measurement is micron.

3.84) What is cla value of surface roughness?

Ans) The cla value is defined as

Cla= 1/L∫Ydx

3.85) What is rms value of surface roughness?

Ans) Rms={√1/L∫y^2 dx}

3.86) Explain the symbol of surface roughness?

Ans) The surface roughness symbol is represented as

a=Roughness value Ra in micrometer

b = Production method, treatment or coating

c = Sampling length

d = Direction of lay

e = Machining allowance

f = other roughness value than Ra



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Ch.4- Design against Static Load

4.1) What is static load?

Ans) A static load is defined as a force that is gradually applied to a mechanical component and which does not change in magnitude or direction with respect to time.

4.2) What is ductile material and give its example?

Ans) A ductile material is the one which has relatively large tensile strain before fracture e.g. copper, tungsten, platinum and Stefan.

4.3) What is brittle material and give its example?

Ans) A brittle material is the one which has relatively small tensile strain before fracture e.g. glass, ceramic, cast iron.

4.4) What is the dividing line between ductile and brittle material?

Ans) A tensile strain of 5% is considered to be the dividing line between ductile and brittle material.

4.5) Distinguish between stress –strain diagrams for ductile and brittle material?

Ans)



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1] Components of brittle material do not exhibit yield point whereas ductile material exhibit yield point(Y).

2] Ductile material has considerable deformation before failurei.e the plastic range in the fig

3] Brittle material exhibit ultimate point B and hence the failure of brittle material is sudden.

4] The deformation of the brittle material is far less than ductile material.

5] Point M represents ultimate tensile stress of the ductile material whereas point B represents ultimate tensile stress of the brittle material.

4.6) What is Elastic Limit ?

Ans) In a stress- strain diagram Elastic limit is the point upto which material will deform under the load and regain its original form when unloaded.

4.7) What is yield Point?

Ans) In a stress- strain diagram yield Point is the point at which material will deform plastically and will not regain its original form when unloaded.

4.8) What are the three basic modes of failures of mechanical component?

Ans) Three basic modes of failures of mechanical component are:

1] Failure by general yielding: i.e. a considerable amount of the component is subjected to plastic deformation and the component loses its usefulness.

2] Failure due to fracture: In this case failure may be sudden without prior warning or it may occur with prior intimation.

3] Failure due to elastic deformation: In thiscase the maximum force acting on the component is limited by maximum permissible deflection.

4.9) Give the examples of mechanical component that fail by elastic deflection?

Ans) Three examples of mechanical component that fail by elastic deflection are beams, transmission shaft supporting gears etc.

4.10) Give the examples of mechanical component that fail by general yielding?

Ans) Knuckle joint ,cotter pin joint ,turn buckle are the mechanical component that fail by general yielding



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4.11) Give the examples of mechanical component that fail by fracture?

Ans) Components made up of cold drawn steel bar and cast iron fail by fracture.

4.12) What is factor of safety?

Ans) The factor of safety is defined as the ratio of failure stress to working stress .or the ratio of the failure load to working load

F.O.S=failure stress ∕ allowable stress

4.13) Why is it necessary to use factor of safety?

Ans) It is necessary to use factor of safety because while designing a component it is necessary to provide sufficient reserve strength in case of accident.

4.14) What are the factors to be considered for determining the magnitude of factor of safety?

Ans) Factors to be considered for determining the magnitude of factor of safety are:

1] Material: Ductile material requires lower F.O.S as compared to brittle material because of uncertainty in its composition.

2] Type of load: if the load is static than stress analysis is simple and hence lower FOS. If the load is fluctuating then stress analysis is complex and hence more FOS.

3] Cost: If the FOS is large, the probability of failure is small but cost increases and vice versa.

4] Quality of production: Inferior quality products require higher FOS and good quality products requires lower FOS since they have fewer defects.

4.15) What is allowable stress?

Ans) The allowable stress is the stress value which is used in design to determine the dimensions of the component.

4.16) How will you find out allowable stress for ductile parts using factor of safety?

Ans) For ductile material the allowable stress



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4.17) How will you find out allowable stress for brittle parts using factor of safety?

Ans) For brittle material allowable stress is

4.18) What is the magnitude of FOS for cast iron component?

Ans) The magnitude of FOS for cast iron component is 3 to 5.

4.19) What is the magnitude of FOS for ductile component?

Ans) The magnitude of FOS for ductile component is1.3 to 1.5.

4.20) What is stress?

Ans) The internal resisting force per unit area of the component is called stress.

4.21) What is strain?

Ans) Strain is deformation per unit length

4.22) What is Hooke’s law?

Ans) The stress is directly proportional to strain, within elastic limit.

4.23) What is tensile stress?

Ans) Tensile stress is ratio of normal tensile force and area

4.24) What is compressive stress?

Ans) Compressive stress is ratio of normal compressive force and area

4.25) What is shear stress?

Ans) When the external force adtig on a component tends to slide the adjacent plane with respect to each other the resulting stress is called shear stress.

4.26) What is the difference between modulus of ductility and modulus of rigidity?

Ans) The modulus of ductility is for the ductile material and the modulus of rigidity is for the brittle material.



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4.27) What is the relationship between modulus of elasticity, modulus of rigidity and Poisson’s ratio?

Ans) The relationship between modulus of elasticity, modulus of rigidity and Poisson’s ratio is given by

E=2G(1+u)

4.28) What is Poisson’s ratio?

Ans) Poisson’s ratio is a ratio of strain in lateral direction to the axial direction.

4.29) When a thick leather belt is bend, crack’s appear on outer surface, while fold’s on the side’, Why?

Ans) When the beam is subjected to a combination of tensile stress on one side of neutral axis and compressive on other so because of stress distribution, a thick leather belt is bend, crack’s appear on outer surface, while fold’s on the side’.

4.30) What is parallel axis theorem for moment of inertia?

Ans) Parallel axis theorem for moment of inertia is given by

Ix1 = Ixg + Ay2

4.31) What is cotter’s joints?

Ans) A cotter joint is used to connect to co-axial rods which are subjected to either axial tensile force or axial compressive force.

4.32) Explain the construction of cotter joint with the help of neat sketch?

Ans) A cotter is wedge shaped piece made of a steel plate the joint is tightened and adjusted by means of a wedge action of the cotter. The socket as well as spigot is provided with a narrow rectangular slot a cotter is tightly fitted in the slot passing through the socket and spigot. The cotter have a uniform thickness and width dimension is slight tapper.

4.33) Where do you use cotter joint? give practical example?

Ans) Cotter joint is used for the joint between the piston rod and the cross head of the steam engine.



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4.34) Explain the principle of wedge action used in cotter joint?

4.35) Why cotter is provided with taper? Why taper is provided only on one side?

Ans) 1)When the cotter is inserted in the slot through the socket and the spigot and pressed by means of hammer it becomes tight due to wedge action.

2)Due to its taper shape it is easy to remove the cotter and dismantle the joint.

4.36) What is the magnitude of taper on the cotter?

Ans) The taper is usually 1 in 24.

4.37) What are the advantages of cotter joint?

Ans) The cotter joint offers following advantages:

The assembly and dismantling of parts of cotter joint are quick and simple. The assembly consist of inserting the spigot end into the socket end and putting the cotter into their common slot. When the cotter is hammered, the rods are drawn together and tightened. Dismantling consist of removing the cotter from the slot by means of hammer.

The wedge action develops a very high tightening force, which prevents loosening of parts in service.



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The joint is simple to design and manufacture.

4.38) What is knuckle joint?

Ans) It is a type of joint used to connect two rods whose axes are either coincide or intersect and lie in one plane. The knuckle joint is used to transmit axial tensile force.

4.39) Explain the construction of knuckle joint with help of neat sketch?

Ans) The construction of a knuckle joint, used to connect to rods A and B subjected to tensile force P, is shown in fig. an eye is formed at the end of rod B, while a fork is formed at the end of rod –A. The eye fits inside the fork and a pin passes through both the fork and the eye. This pin is secured in its place by means of split-pin. Due to this type of construction, a knuckle joint is some times called as a fork-pin joint.

4.40) Where do you use knuckle joint? Give practical examples.

Ans) The knuckle joint is used to:

Joints between the tie bars in roof trusses.

Joints between the links of a suspension bridge.

Joints in valve mechanisms of a reciprocating engine.

Fulcrum for levers.

4.41) What are the advantages of knuckle joint?

Ans) The knuckle joint offers the following advantages:

The joint is simple two design and manufacture

There are a few parts in the knuckle joint which reduces cost and improves reliability.



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The assembly or dismantling of the parts of knuckle joint is quick and simple. The assembly consists of inserting the eye of one rod inside the fork of the other rod and putting the pin in there common hole and finally putting the split-pin to hold the pin. Dismantling consist of removing the slit-pin and taking the pin out of the eye and the fork.

4.42) What is the difference between normal stress and shear stress?

Ans) The normal stress is perpendicular to the area under consideration, while the shear stress acts over the area.

4.43) Explain the construction of Mohr's circle diagram to find out principal stresses.

Ans) It is the graphical method for the representation of stresses. The following conventions are used to construct the Mohr’s circle:

The normal stresses and the principal stresses are plotted on the abscissa. The tensile stress considered as positive, compressive stress as negative to its left.

The shear stresses and the principal shear stress are

plotted on the ordinate. A pair of shear

stresses is considered as positive if they tend

to rotate in anticlockwise.

MOHR’S CIRCLE



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4.44) What is the advantages of using the theories of elastic failures?

Ans) With the help of elastic failure theory the data obtained in the tension test can be used to determine the dimensions of the components, irrespective of the nature of stresses induced in the component due to complex loads.

4.45) What are the important theories of elastic failure?

Ans) The principal theories of elastic failure are as follows:

Maximum principal stress theory ( Rankine’s theory).

Maximum shear stress theory (Coulomb, Tresca and Guest’s theory).

Distortion theory (Huber von Mises and Hencky’s theory).

Maximum strain theory (St. Venant’s theory).

Maximum total strain energy theory (Haigh’s theory).

4.46) State maximum principal stress theory of failure.

Ans) The theory states:

“ That the failure of mechanical components subjected to bi-axial or tri-axial stresses occurs when the maximum principal stress reaches the yield or ultimate strength of the material”.

4.47) Where do you use maximum principal stress theory of failure?

Ans) The maximum principal stress theory gives good predictions for brittle materials. However, it is not recommended for ductile materials.

4.48) State maximum shear stress theory of failure.

Ans) The maximum shear stress theory states that the failure of a mechanical component subjected to bi-axial or tri-axial stresses occurs when the maximum shear stress at any point in the component becomes equal to the maximum shear stress in the standard specimen of the tension test, when yielding starts.

4.49) Where do you use maximum shear stress theory of failure?

Ans) The maximum shear stress theory of failure is widely used by designers for predicting the failure of components, which are made of ductile materials, like transmission shaft.

4.50) State distortion energy theory of failure.



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Ans) The distortion energy theory is also known as the Huber von Mises and Hencky’s theory. The theory states that the failure of a mechanical component subjected to bi-axial or tri-axial stresses occurs when the strain energy of distortion per unit volume at any point in the component, becomes equal to the strain energy of distortion per unit volume in the standard specimen of tension-test, when yielding starts.

4.51) Where do you use distortion energy theory of failure?

Ans) Distortion energy theory of failure is in better agreement for predicting of the failure of a ductile component then any other theory of failure.

4.52) What is lever? Explain the principle on which it works.

Ans) A lever is defined as a mechanical device in the form of a rigid bar pivoted about the fulcrum to multiply or transfer the force. It works on the principle of moments.

Fig(a) : a lever

4.53) What is mechanical advantage?

Ans) The ratio of load to effort, i.e (F/P) is called as the mechanical advantage of the lever.

4.54) What is leverage?

Ans) The ratio of effort arm to the load arm, i.e (l1/l2) is called the leverage

4.55) What is first type of lever? Give its examples.

Ans) In the first type of lever, the fulcrum is located between the load and the effort, as shown in fig. In this case, the effort arm can be kept less than the load arm or equal to the load arm or more than the load arm accordingly, the mechanical advantages will vary in the following way:

When d 1<le



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Mechanical advantage < 1

When d 1=de

Mechanical advantage = 1

When d 1>de

Mechanical advantage > 1

Usually, the effort arm is kept more than the load arm to get mechanical advantage. This type of lever is used in applications like the rocker arm for overhead valves of internal combustion engine, bell crank lever in railway signal mechanism and lever of hand pumps.

4.56) What is second type of lever ? Give its examples.

Ans) In the second type of lever,the load is located between the fulcrum and the effort. The effort arm is always more than the load arm and mechanical advantage is more than 1.This type of lever is used in safety valve mounted on the boilers

4.57) What is third type of lever ? Give its examples.

Ans) In the third type of lever,the effortis located between the load and the fulcrum. The load arm is always more than the effort arm and mechanical advantage is less than 1. A picking fork is an example of this type of lever.

4.58) What type of stress is induced in cross section of lever ?

Ans) The cross section of lever is designed on the basis of bending stresses.

4.59) Why are lever usually tapered ?

Ans) Due to the variation of bending moment along the lever arm. So the cross section of arm is usually tapered from the boss of the fulcrum to the end.

4.60) What is a fracture mechanics ?

Ans) Fracture mechanics is the science of predicting the influence of cracks crack like defects on the brittle fracture of components.

4.61) What is stress intensity factor in fracture mechanics ?

Ans) The stress intensity factor specifies the stres intensity at the tip of the crack.



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4.62) What is fracture toughness in fracture mechanics ?

Ans) The fracture toughness is the critical value os stress intensity at which crack extension occurs.

4.63) What is the difference between stress intensity factor and fracture toughness in fracture mechanics ?

Ans) The stress intensity factor represents the stress level at the tip of the crack in the machine parts. On the other hand, fracture toughnessis the highest stress intensity that the part can withstand without fracture at the crack.

4.64) What are the three modes of crack propagation in fracture mechanics ?

Ans) Mode 1—Opening or tensile mode.

Mode 2—Sliding or in-plane shearing mode.

Mode 3—Tearing mode.

4.65) Whatis curved beam? Give practical examples of machine conponents made of curved beams.

Ans) A curved beams is defined as a beam in which the neutral axis in unloading condition is curved instead of straight. The crane hook is an example of curved beams.

4.66) Distinguish stress distribution between curved and straight beams.

Ans) 1. The neutral and centroidal axis of the straight beams are coincident.However, the curved beams the neutral axis is shifted towards the centre of curvature.

2. The bending stress,instraight beam, vary linearly with the distance from the neutral axis.However ,in curved beams, the stress distribution is hyperbolic.

4.67) What are the components where thermal stressesare considered ?

Ans) The thermal stresses are important in design of components like shrinkage assemblies,compound cylinder,pipes lines,parts of I.C engines etc.

4.68) What are the residual stress ?

Ans) Residual stress are also called internal stress or locked-in stress.This stresses are independent of external forces.



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4.69) What are the causes of residual stresses ?

Ans) These stresses are caused due to manufacturing process such as casting,forging, rolling, extrusion,cold working processesand also in heat treatment processes like quenching.

4.70) When are residual stresses benificial ?

Ans) If the residual stresses are opposite to load stress and subtract, they are benificial.

4.71) When are residual stresses harmful ?

Ans) If the residual stresses add to the load stresses, they are harmful.



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Ch.5 - Fundamentals of Machine Design

5.1) What is stress concentration ?

Ans) Stress concentration is defined as the localization of high stresses due to the irregularities present in the component and abrupt changes of the cross section.

5.2) How will you account for stress concentration in design of machine parts ?

Ans) Stress concentration must be reduced in order to design a machine components by providing additional notches and holes in the tension member or drilling additional holes in shaft or using bolts of uniform strength.

5.3) What is stress concentration factor ?

Ans) Stress concentration factor is defined as the ratio of the highest value of actual stress near discontinuity to nominal stress obtained by elementary equation for minimum cross-section.

5.4) What are the causes of stress concentration ?

Ans) 1.Variation in properties of material.

2.Load application.

3.Abrupt changes in cross section.

4.Discontinuities in the components.

5.5) What is the effect of stress concentration on ductile material?

Ans) When the ductile material is subjected to fluctuating load, the stress at discontinuities may exceed the endurance limit and component may fail by fatigue.

5.6) What is the effect of stress concentration on brittle material?

Ans) When the brittle material with discontinuities is subjected to load the local stress at the discontinuity reaches the fracture strength and a crack is formed thus failing the part of the component quickly.

5.7) What are the methods of reducing stress concentration?

Ans) Fillet Radius, Undercutting, Providing Notches, Additional Holes are few methods for reducing stress concentration.



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5.8) How will you reduce stress conc. in shaft with keyway ?

Ans) Drilling an additional hole in shaft with keyways helps in reducing Stress concentration.

5.9) How will you reduce stress concentration in threaded parts?

Ans) In order to reduce stress concentration in threaded parts the shank diameter is reduced and made equal to core diameter of the threads.

5.10) What is fluctuating Stress ?

Ans) Fluctuating stress is a type of stress in which the Mean stress within a body is not equal to zero .

5.11) What is repeated Stress ?

Ans) Repeated stress is a type of cyclic stress which varies in sinusoidal manner but variation is from zero to maximum values.

5.12) What is reversed stress ?

Ans) Reversed Stress is a type cyclic stress which varies in sinusoidal manner with respect to time , but it has zero mean stress.

5.13) What is Fatigue failure ?

Ans) Fatigue failure is define as delayed fracture under cyclic loading.

5.14) What are the machine components that fail by fatigue?

Ans) The machine components that fail by fatigue are Transmission Shaft, connecting rod, gears, ball bearings, suspensions spring.

5.15) What is the difference bet. failure due to static load and fatigue failure ?

Ans) The Fatigue failure begins with crack at some point in the materials whereas in static load failure there is considerable plastic flow prior to the fracture .

5.16) What is endurance limit ?

Ans) A stress below which Fatigue Failure does not occur regardless of number stress cycle.



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5.17) What is fatigue life ?

Ans) Fatigue life is the number of stress cycles of a specified character that a material sustains before failure of a specified nature occurs.

5.18) Explain the principle of rotating beam fatigue testing machine ?

Ans) In Rotating Beam Fatigue Testing Machine a highly polished specimen of 0.3 inches in diameter is subjected to pure bending stresses that are alternated by rotating the specimen. The rotation takes place at 1725 rpm.

5.19) What is S-N curve ?

Ans) In high-cycle fatigue situations, materials performance is commonly characterize by an S-N curve, also known as a Wöhler curve .This is a graph of the magnitude of a cyclic stress (S) against the logarithmic scale of cycles to Failure (N).

5.20) What is the difference bet. S-N curve of ferrous and non ferrous metal ?

Ans) The S-N curve for ferrous material becomes asymptotic at 10^6 cycles, which indicates the stress against infinite no. of stress cycle whereas for non ferrous material like Aluminum the S-N curve slopes gradually even after 10^6 cycles.

5.21) What is low cycle fatigue ?

Ans) When the number of stress cycle are less then 1000 the Fatigue failure is said to be low cycle fatigue. It involves plastic Yielding at localized areas of the component.

5.22) Give practical example of low cycle fatigue failure ?

Ans) Failure of studs on truck wheels, failure of setscrews for locating gears on shafts, failure of devices like missiles are the practical example of low cycle fatigue .

5.23) What is high cycle fatigue ?

Ans) When the fatigue occurs above 103 cycles (usually 104 or more), it is usually called High-cycle fatigue. The material is subject to lower loads, usually less than 2/3 of the yield stress. The deformation is in elastic range. The fatigue life is "high-cycle" (103 ~ 106).

5.24) Give Example of high cycle fatigue failure ?



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Ans) The failure of Springs, ball bearings and gears that are subjected to fluctuating stress are the practical examples of high cycle fatigue.

5.25) What is fatigue stress concentration Factor ?

Ans) Stress Concentration factor is the ratio of Endurance Limit of a Notch free specimen to the Endurance Limit of notched specimen.



Machine Design


Ch.6- power screws

6.1) What is power screw?

Ans) A power screw is a mechanical device used for converting rotary motion into linear motion and transmitting power.Power screw is also called translation screw.

6.2) What are the applications of power screw?

Ans) The main applications of power screw are as follows:

1. To raise the load e.g. screw jack

2. To obtain the accurate motion in machining operation e.g. lead screw of lathe.

3. To clamp the work piece e.g. vice

4. To load the specimen e.g. UTM

6.3) What are the advantages of power screws?

Ans) 1. A power screw has large load carrying capacity.

2. The overall dimensions of the power screw are small, resulting in compact

construction.

3. A power screw is simple to design.

6.4) What are disadvantages of power screw?

Ans) 1. A power screw has very poor efficiency as low as 40%. Therefore, it is not used in continuous power transmission in machine tools, with the exception of the lead screw.

2. High friction in threads causes rapid wear of the scrwew or the nut

6.5) What are the types of threads for power screw?

Ans) There are two popular types of threads used for power screws, viz, square and

ISO metric trapezoidal.

6.6) Why are V threads not used in power screws?

Ans) The threads used for fastening purpose such as V threads. The purpose of

fastening threads is to provide high frictional force, which lessens the possibility of



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loosening the parts assembled by threaded joint. On the other hand, the purpose of power transmission threads is to reduce friction between the screw and nut. Therefore, V threads are not suitable for power screws.

6.7) Why are square threads preferred to V threads in power screw?

Ans) The threads used for fastening purpose such as V threads. The purpose of

fastening threads is to provide high frictional force, which lessens the possibility of loosening the parts assembled by threaded joint. On the other hand, the purpose of power transmission threads is to reduce friction between the screw and nut. Therefore, V threads are not suitable for power screws. Hence square threads are preferred in power screw.

6.8) What are the advantages of square threads over trapezoidal threads?

Ans) 1. The efficiency of square threads is more than that of trapezoidal threads

2. There is no radial pressure or side thrust on the nut. This radial pressure is

called ‘bursting’ pressure on the nut

6.9) What are the disadvantages of square threads compared with trapezoidal threads?

Ans) 1. Square threads are difficult to manufacture. They are usually turned on a lathe

with a single-point cutting tool

2. The strength of a screw depends upon the thread thickness at the core

diameter.

6.10) What are the advantages of trapezoidal threads over square threads?

Ans) 1. Trapezoidal threads are manufactured on a thread milling machine. It employs

a multipoint cutting tool.

2. A trapezoidal thread has mora thickness at the core diameter than a square

thread.

6.11) What are the disadvantages of trapezoidal threads compared with square

threads?

Ans) 1. The efficiency of trqpezoidal threads is less than that of square threads.

2. Trapezoidal threads result in side thrust or radial pressure on the nut.



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6.12) What is acme threads? What is the difference between acme and trapezoidal

threads?

Ans) Acme threads is a special type trapezoidal threads. Trapezoidal and acme threads are identical in all respects except the thread angle. In an acme thread, the thread angle is 29o instead of 30o.

6.13) What are the advantages of buttress threads?

Ans) 1. It has higher efficiency compared with trapezoidal threads.

2. It can be economically manufactured on a thread milling machine

3. The axial wear at the thread surface can be compensated by means of a split-

type nut.

6.14) What are the disadvantages of buttress threads?

Ans) It can transmit power and motion only in one direction.

6.15) What are the application of square threads?

Ans) Square threads are used for screw jacks, presses and clamping devices.

6.16) What are the application of trapezoidal threads?

Ans) Trapezoidal threads are used for lead screw and other power transmission devices in machine tools.

6.17) What are the application of buttress threads?

Ans) Buttress threads are used in vices, where force is applied only in one direction.

6.18) How will you designate square threads?

Ans) Sq30x6

6.19) How will you designate trapezoidal threads?

Ans) Tr40x7

6.20) How will you designate multiple-start trapezoidal threads?



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Ans) Tr40x14(P7)

6.21) What are multiple start screws?

Ans) Multiple start screws are screws having two or more threads cut side by side.

6.22) What are the advantages of multiple start screws?

Ans) 1 It provides large axial motion per revolution of the screw. This increases the

travelling speed of the sliding member

2 The efficiency of a multi-threaded screw is more than a single-threaded screw

due to helix angle.

6.23) What are the disadvantages of multiple start screws?

Ans) The disadvantages of multiple start screws are as follows:

1 The mechanical advantage obtained with multiple threaded screws is lower

than that of single threaded screw. Therefore, the effort required to raise a

particular load or apply a particular force is more.

2 It is likely that, the self-locking property may be lost in multi-threaded screw.

The resulting condition is dangerous in certain applications like screw jack

where load may descend on its own.

6.24) What are the applications of multiple start screws?

Ans) Multiple threaded screws are used on high-speed actuators and sluice valves.

6.25) What is the pitch of screw?

Ans) The is defined as the distance, measured parallel to the axis of the screw, from

a point on one thread to the corresponding point on the adjacent thread.

6.26) What is the lead of screw?

Ans) The lead is defined as a distance, measured parallel to the axis of the screw

that the nut will advance in one revolution of the screw.

6.27) What is the nominal diameter of screw?



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Ans) Nominal diameter is the largest diameter of the screw. It is also called the major

diameter.

6.28) What is the helix angle of thread?

Ans) The helix angle is define as the angle made by the helix if the thread with a

plane perpendicular to the axis of the screw. It is also called lead angle.

6.29) Write down the relationship between lead, pitch and number of starts in power

screw.

Ans) The relation between lead, pitch and number of starts in power screw is given

as: l = n*p

where, l - lead of screw

p - pitch of screw

n - number of starts

6.30) Write down the relationship between helix angle, mean diameter and lead of

screw.

Ans) The relation between helix angle, mean diameter and lead of screw is given as:

tan = l/ *dm

where, - helix angle of screw

dm - mean diameter of screw

l - lead of screw

6.31) Write down the relationship between load being raised, the effort applied, helix

and friction angles in power screw.

Ans) The relation between load raised, the effort applied, helix and friction angles in

power screw is given by P = W* )

6.32) Write down the relationship between load being lowered, the effort applied,

helix and friction angles in power screw.

Ans) The relation between load lowered, the effort applied, helix and friction angles

in power screw is given as:



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P = W*

6.33) What is overhauling of power screw? What is the condition for overhauling?

Ans) A condition in which no force is required to lower the load and the load itself

begins to turn the screw and descend down, unless a restraining torque is

applied. This condition is called as overhauling of power screw.

It occurs when, . (torque required to lower the load is negative)

6.34) What is self-locking of power screw? What is the condition for self-locking?

Ans) A condition in which the load will not turn the screw and will not descend on its own unless effort is applied. This condition is called as self-locking of power screw.

It occurs when, . (torque required to lower the load is positive)

6.35) State the applications where self-locking is essential.

Ans) Self-locking condition is essential in applications like screw jack.

6.36) Write down the expression for efficiency of square threaded screw.

Ans) The efficiency of square threaded screw is given as:

6.37) What is the effect of helix angle on efficiency of square threaded screw?

Ans) The efficiency of square threaded screw depends upon the helix angle.

1. The efficiency of square threaded screw increases rapidly up to helix angle of

200 .

2. The efficiency is maximum, when the helix angle is between 40 - 450 .

3. The efficiency decreases after the maximum value is reached.

4. The efficiency decreases rapidly when the helix angle exceeds 600 .

6.38) What is the effect of lead on efficiency of square threaded screw?

Ans) The efficiency of square threaded screw increases with increase in lead of

screw and vice versa.



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6.39) What are the two methods to increase the efficiency of square threaded screw?

Ans) The two methods to increase the efficiency of square threaded screw are as

follows:

1. Reduce the coefficient of friction between the screw and the nut by proper

lubrication; and

2. Increase the helix angle up to 40 – 450 by using multiple start threads.

6.40) Why the efficiency of self-locking square threaded screw is less than 50%?

Ans) The efficiency of square threaded screw is given as:

η = ………..(a)

For self-locking screw,

Substituting the limiting value in eq. (a)

η or η

Substituting,

/1-tan2

In above expression,

η tan2 /2]

Therefore, efficiency of self-locking square threaded screw is less than ½ or 50%.

6.41) What is the effective coefficient of friction in trapezoidal threads?

Ans) The effective coefficient of friction in trapezoidal threads is taken as ( .

6.42) Write down the expression for efficiency of trapezoidal threaded screw.

Ans) The efficiency of trapezoidal threaded screw is given as:

η

6.43) What is collar friction?

Ans) There is a relative motion between cup and collar at the annual interface from inner to outer diameter resulting in friction which is called collar friction.



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6.44) What are the factor upon which the coefficient of friction in power screw depends?

Ans) The factors are workmanship in cutting the threads and the type of lubricant.

6.45) Name the materials for power screw components?

Ans) Material combinations are as follows

Soft-steel –cast iron, hardened steel – cast iron, soft steel – bronze, hardened steel –bronze.

6.46) What are the types of stresses induced in power screw?

Ans) Torsional shear stress, direct compressive stress, transverse shear stress.

6.47) What is differential screw?

Ans) A differential screw is a mechanism used for making small, precise adjustments to the spacing between two objects (such as in focusing a microscope). It uses a "nut" with two screws, one entering each end. The "heads" of the screws are fixed to the objects whose spacing is to be adjusted.

6.48) What is compound screw?

Ans) It is a mechanical device consisting of two screws in series arranged in such a way that the resultant motion is a sum of individual motion of two screws.

6.49) Where do you use differential & compound screws?

Ans) Differential screw is used for focusing a microscope whereas compound screw is used in various lathes and complex machines.

6.50) What is recirculating ball screw?

Ans) It is a mechanical linear actuator that translates rotational motion to linear motion with little friction.

6.51) What are the advantages of recirculating ball screw?

Ans) Advantages .


http://en.wikipedia.org/wiki/Microscope

http://en.wikipedia.org/wiki/Linear_actuator

http://en.wikipedia.org/wiki/Friction


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Low friction in ball screws yields high mechanical efficiency compared to alternatives. A typical ball screw may be 90 percent efficient, versus 50 percent efficiency of an Acme lead screw of equal size. The higher cost of ball screws may thus be offset by lower power requirements for the same net performance.

6.52) What are the disadvantages of recirculating ball screw

Ans) Disadvantages.

Depending upon their lead angle, ball screws can be back-driven due to their low internal friction (i.e. the screw shaft can be driven linearly to rotate the ball nut). They are usually undesirable for hand-fed machine tools, as the stiffness of a servo motor is required to keep the cutter from grabbing the work and self feeding, that is, where the cutter and work piece exceed the optimum federate and effectively jam or crash together, ruining the cutter and work piece.

6.53) What are the applications of recirculating ball screw?

Ans) Ball screws are used in aircraft and missiles to move control surfaces, especially for electric fly by wire and in automobile power steering to translate rotary motion from an electric motor to axial motion of the steering rack. They are also used in machine tools, robots and precision assembly equipment. High precision ball screws are used in steppers for semiconductor manufacturing.

6.54) Why is thrust ball bearings use at the collar in the power screws?

Ans) The sliding friction is replaced by rolling friction, and the collar friction torque becomes negligible.

6.55) In hand operated fly press overhauling screw is used, why?

Ans) It is used so that the load will begin to turn the screw and decend down, unless a restraining of the screw.

6.56) What are the applications of high efficiency power screw?

Ans) The applications where high efficiency is expected are power transmission applications such as lead screw, presses.

6.57) What are the applications of low efficiency power screw?

Ans) The applications where low efficiency is required for purpose of selflocking are screw jacks, clamps, vices.


http://en.wikipedia.org/wiki/Mechanical_efficiency

http://en.wikipedia.org/wiki/Machine_tool

http://en.wikipedia.org/wiki/Servo_motor

http://en.wikipedia.org/wiki/Fly_by_wire

http://en.wikipedia.org/wiki/Power_steering

http://en.wikipedia.org/wiki/Machine_tool

http://en.wikipedia.org/wiki/Robot

http://en.wikipedia.org/wiki/Stepper

http://en.wikipedia.org/wiki/Semiconductor_manufacturing


Machine Design


6.58) What are the factors upon which the thread bearing pressure in power screw depends?

Ans) It depends upon the material of screw and the nut and the rubbing velocity.

6.59) Why is separate nut preferred to integral nut with body of screw jack?

Ans) It is preffered so that the lifting of heavy loads could be handled easily.



Machine Design


Ch.7- Design of Bolted Joint

7.01) What is threaded joint?

Ans) A joining of parts by means of threads, A mechanical joint between threaded pipes or between a threaded pipe and threaded fitting.

7.2) What are the advantages of threaded joints?

Ans) Advantages.

They are easily disassembled, as opposed to something like riveting or welding, which requires cutting.

You can put a bolt in a blind hole (one that doesn't go all the way through the material); you can't use a rivet.

Bolts offer much better joint quality than a screw, mostly because the threads are more tightly controlled.

7.3) What are the disadvantages of threaded joint?

Ans) Disadvantages.

Corrosion between a bolt and the parent material should be considered. This may not be a problem with welding and adhesive joints if the parent materials being welded are compatible.

Bolted joints require a gasket to seal a joint. A weld (if done properly) will be leak-proof.

Bolted joints aren't so easy after all - I know of robots that weld, but the manual dexterity needed to install a bolt still requires a human touch.

7.44) What are the advantages of V-threads?

Ans) The advantages of V-threads are, they result in higher friction, which lessen possibility of loosening; they have higher strength due to increased thread thickness at core diameter; and they are more convenient to manufacture.

7.45) Why the roots and crests are rounded in vee threads?

Ans) The crests and roots are rounded in vee threads because, it reduces stress concentration; it increases the tool life of thread cutting tool; it reduces damaging of thread by denting; it prevents leakage in fluid tight threads.



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7.46) What are the advantages of coarse threads?

Ans) Coarse threads offer the following advantages: Static load carrying capacity is higher; they are easier to cut than fine threads; errors in manufacture & wear have less effect on strength; they have more even stress distribution.

7.47) What are the advantages of fine threads?

Ans) Fine threads offer the following advantages: they have greater strength when subjected to fluctuating load; they have greater resistance to unscrewing due to lower helix angle; they are more dependable than threads with coarse pitch in respect of self-unscrewing.

7.48) What are the applications of coarse threads?

Ans) Coarse threads are recommended for general industrial applications, which are free from vibrations.

7.49) What are the applications of fine threads?

Ans) Fine threads are used for the following applications: when parts are subjected to dynamic loads and vibrations like automobile applications; hollow thin walled parts where coarse threads are liable to weaken the wall considerably.

7.50) How will you designate ISO metric coarse threads?

Ans) A screw thread of coarse series is designated by the letter ‘M’ followed by the value of the nominal diameter in mm. For example, M 12.

7.51) How will you designate ISO metric fine threads?

Ans) A screw thread of fine series is designated by the letter ‘M’ followed by the values of the nominal diameter and pitch in mm and separated by the symbol ‘x’. For example, M 12x1.25.

7.52) What are the materials for bolts and screws?

Ans) Lightly loaded small bolts, studs and nuts are made of free cutting steel. High strength bolts are made of plain carbon steels like 40C8 or 45C8 or alloy steels like 35Mn6Mo3, 40Cr4Mo2,etc.

7.53) What are the methods to make bolts and screws?



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Ans) The head of the bolt or screw is made by the upsetting process. The head is cold formed for diameters upto 20mm; for larger diameters hot forming is employed.

7.54) Why thread rolling is superior to thread cutting?

Ans) Threads formed by thread rolling have outside diameter of thread is more than the bar stock on which it was rolled. Hence thread rolling is superior method of making threads.

7.55) The threads are equally strong in failure by shear and failure by tension if the height of nut is 0.4 times of nominal diameter. Why?

7.56) What is turnbuckle?

Ans) A turnbuckle, stretching screw or bottlescrew is a device for adjusting the tension or length of ropes, cables, tie rods, and other tensioning systems.

7.57) What are the applications of turnbuckle?

Ans) Turnbuckles are most commonly used in applications which require a great deal of tension; they can range in mass from about ten grams for thin cable used in a garden fence, to thousands of kilograms for structural elements in buildings and suspension bridges. They are widely used in aircrafts, for tensioning ships riggings and lashings, etc.

7.58) What do you understand by hard and soft gaskets?

Ans) "Soft gaskets" consist of rubber, while "hard gaskets" consist of metal coated with graphite.

7.59) Why are connecting rods bolt tightened with initial tension greater than external load?

Ans) When the connecting rod bolts are tightened up with initial pre-load greater than external load, the total load on the bolt will be almost static and the bolt can be designed on the basis of static failure; the resultant load on bolt will be affected by external load, which is fluctuating and it is required to design the bolt the bolt on the basis of endurance limit to avoid fatigue failure.

7.60) Which of the two should be more: initial tightening load or external load in bolted joints?



Machine Design


Ans) In case of joints with fluctuating loads, initial tension load is greater than external load in bolted joints.

7.61) What are the practical applications of uniform strength bolts?

Ans) Bolts of uniform strengths are used to reduce stress concentration at the threads and reduce shear stress at the core diameter which is usually lesser than shank diameter.

7.62) What are the advantages of pre loading of bolts?

Ans) Initial pre-load of bolts, the total load on the bolt will be almost static and the bolt can be designed on the basis of static failure.

7.63) What is the function of plain washer in bolted joints?

Ans) The two most common proper purposes are: To distribute the pressure of the nut or bolt evenly over the part being secured, reducing the chance of damage thereto, and to provide a smooth surface for the nut or bolt to bear on, making it less likely to loosen as a result of an uneven fastening surface.

7.64) Why usually bolts are subjected to tensile loading and rivets to shear loading?

Ans) Bolts are usually subjected to tensile loading because it offers high resisting strength in tension than in shear and rivets offers high resisting strength in shear than in tension.

7.65) What are different types of stresses to which a bolt is subjected?

Ans) A bolt is subjected to tensile stress, compressive stress and shear stress.

7.66) What is effect of gasket on bolt load?

Ans) When the gasket is too soft, then the resultant load on the bolt is the sum of initial tension and external load

When the gasket is too hard, then the resultant on the bolt is initial tension only.

7.67) What are the method of increasing fatigue strength in a bolted joint?

Ans) For increasing the fatigue strength in a bolted joint, the threads should be made fine and rolling method for making thread should be used instead of cutting method.



Machine Design


7.68) What are the method of increasing the shock absorbing capacity of bolt?

Ans) There are two methods for the shock absorbing capacity of bolt:-

Reduce the shank diameter to core diameter of threads or even less.

Increase the length of the shank portion of the bolt.



Machine Design


Ch.8- Design of Welded Joint

8.1) What are the advantages of welded joints compared with riveted joints?

Ans) Welded assembly results in lightweight construction, low cost, easy and economical modification, tight and leak proof assembly and less production time compared to riveted joints.

There is also no stress concentration in welded assembly and the strength of welded joint is also high.

8.2) What are the advantages of welded assemblies compared with cast iron structures?

Ans) Welded assemblies are lighter in weight, have low cost and can be more easily machined compared to cast iron structures.

The designer has more freedom and flexibility in the design of welded assemblies as compared to the cast iron structures.

8.3) What are the disadvantages of welded joints?

Ans) As compared to cast iron structures welded structures have poor vibration damping capacity.

Welding results in a thermal distortion of the parts, thereby inducing residual stresses.

8.4) What is the cause of residual stresses in welded joints? How are they relieved?

Ans) Welded joints are subjected to residual stresses due to non uniform heating of the parts being joined.

The following two methods can relieve residual stresses:-

Preheating of the weld area to retard cooling of the metal in the vicinity of the joint. By using proper heat treatment in temperature range of 550o to 675o.

8.5) What is reinforcement in weld? What are its advantages and disadvantages?

Ans) Reinforcement in weld is provided for compensating for any flaws in the weld.

Its advantage is that, it provides a complete cross sectional area to a joint.

Its disadvantage is that, that due reinforcement there is stress concentration in joints.



Machine Design


8.6) What is butt joint?

Ans) A butt joint is defined as a joint between two components lying approximately in the same plane.

8.7) What are the types of butt joints?

Ans) Types of butt joints are:-

Square butt joints.

V-butt joints.

U-butt joints.

Double V-butt joints.

V-butt joint with backing strip.

8.8) What is fillet joint?

Ans) A fillet joint or lap joint is a joint between two overlapping components.

8.9) What is transverse fillet weld?

Ans) A transverse fillet weld is one in which the direction of the weld is perpendicular to the direction of the force acting on the joint.

8.10) What is parallel fillet weld?

Ans) A parallel fillet weld is one in which the direction of the weld is parallel to the direction of the force acting on the joint.

8.11) What are the advantages of triangular cross-section normal weld over convex cross-section welds?

Ans) A triangular cross-section normal weld requires less filler material and labour and stress concentration is also less as compared to convex cross-section welds.

8.12) What is leg of fillet weld?

Ans) A leg of a fillet is the two equal sides in the fillet weld.

8.13) What is throat of fillet weld?



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Ans) The throat of the fillet weld is the minimum cross section of the weld located at 45o to the leg dimension.

8.14) What is relationship between leg and throat of fillet weld?

Ans) Throat of the fillet weld (t) = cosine (45o)*leg of fillet weld (h).

8.15) Which plane is subjected to maximum shear stress in case of parallel fillet welds?

Ans) The plane at an inclination 45o to the leg dimension is subjected to maximum shear stress in case of parallel fillet weld.

8.16) Which plane is subjected to maximum shear stress in case of transverse fillet welds?

Ans) The plane subjected to maximum shear stress in case of transverse fillet welds is the plane which makes an angle of 67.5 O with the base plate.

8.17) What are the basic symbols of welding?

Ans)

8.18) What are permanent joints? Give their examples.



Machine Design


Ans) Permanent joints are those joints which cannot be disassembled without damaging the parts of the assembly. Riveted and welded joints are examples of permanent joints.

8.19) What are separable joints? Give their examples.

Ans) Separable joints are those joints which allow disassembly and reassembly without damaging the assembled parts. For eg. Bolted joints, cotter joints, splined connections.

8.20) In recent days, why have riveted joints been replaced by welded joints?

Ans) Riveted joints are replaced by welded joints because they are expensive as they have additional operations to be performed on them, more weight, more noise in d process, stress concentration, material cost and vibrations due to the fits in a rivet.

8.21) State the difference between hot and cold riveting.

Ans) In hot riveting the shank is heated upto 1000 OC till it becomes bright red and then it is hammered to flatten it out. In cold riveting there is no heating.

Cold riveting requires more force to flatten out the shank as compared to hot riveting

8.22) Application of riveted joints

Ans) Metal framed buildings and structures such as the Eiffel Tower, Shukhov Tower and the Sydney Harbor Bridge were generally held together by riveting. Also automobile chassis were riveted. Riveting is still widely used in applications where light weight and high strength are critical, such as in an aircraft.

8.24) What are the types of rivet heads.?

Ans)



Machine Design


8.25) What is a lap joint?

Ans) In woodworking or metal fitting, a lap joint is a technique for joining two pieces of material by overlapping them.

8.26) What is a single riveted lap joint?

Ans) The lap joints which are joined by only one row of rivets are called single riveted lap joints.

8.27) What is a double riveted lap joint?

Ans) The lap joints which are joined bye 2 rows of rivets are called double riveted lap joint.

8.28) What is a chain riveted lap joint?

Ans) A chain riveted lap joint is a joint in which rivets are arranged in such a way that rivets in different rows are located opposite to each other.

8.29) What is a zig zag riveted lap joint?

Ans) A zig-zag riveted joint is a joint in which the rivets are arranged in a such a way taht every rivet in a row is located in the middle of two rivets in the adjacent rows.

8.30) What is a butt joint?

Ans) A joint between two plates, planks, bars, sections, etc., when the components are butted together and do not overlap or interlock. The joint may be strapped



Machine Design


with jointing plates laid across it or welded (butt weld) sometimes shortened to butt.

8.31) What is the advantage of butt joint over lap joint?

Ans) The advantages of butt joint over lap joint are, it results in uniform surface, it has more strength and its easy to make a butt joint.

8.32) What are the disadvantages of butt joint?

Ans) The disadvantages of butt joints are as follows. The first of these is that they are especially sensitive to weld defects. Because all of the forces on the joint are absorbed by the weld, defects such as porosity, inclusions, cracks, etc, can cause easily cause the joint to fail catastrophically. A second disadvantage of the butt weld is that it is usually not self-aligning. Whereas some other joint types will hold together before welding, the butt joint will not. In many cases this greatly increases the complexity of the fixturing necessary to hold the pieces to be welded in place before and during the welding processes. A third disadvantage of the butt weld is that it is nearly impossible to butt weld very thin materials, due to the fact that aligning the faces properly is very difficult

8.33) What is the most common material for rivets?

Ans) The materials used to make rivets are hot rolled steel and high tensile stell. The chemical composition is as follows.

C= 0.23%

S=0.05%

P=0.05%

8.34) Define efficiency of a joint

Ans) The efficiency of the riveted joint is defined as the ration of strength of riveted joint to the strength of unriveted solid plate.

8.35) What is caulking?

Ans) Caulking is one of several different processes to seal joints or seams in various structures and certain types of piping.

8.36) What is Fullering?


http://en.wikipedia.org/wiki/Seal_(mechanical)


Machine Design


Ans) In metalworking, a fuller is a tool used to form metal when hot. The fuller has a rounded, either cylindrical or parabolic, nose, and may either have a handle (an "upper fuller") or a shank (a "lower fuller"). The shank of the lower fuller allows the fuller to be inserted into the hardy hole of the anvil. Upper fullers furthermore come in "straight" or "cross" varieties, depending on the orientation of the handle relative to the face.



Machine Design


Ch.9- Design of Shaft

9.1) What is the function of the transmission shaft?

Ans) The term transmitting shaft usually refers to a rotating machine element, circular in cross section, which supports transmission elements like gears, pulley, sprockets and transmits power.

9.2) Why is transmission shaft stepped?

Ans) The steps on the transmission shaft provides shoulder for positioning transmission elements like gears, pulleys and bearings.

9.3) What is a fillet? Why is the shaft provided with fillet?

Ans) The rounded off portion between two cross sections of different diameters is called fillet. The fillet radius is provided to reduce the effect of stress concentration.

9.4) How are commercial shafts made?

Ans) Commercial shafts are made of low carbon steels. They are produced by hot rolling and finished to size either by cold drawing or by turning and grinding.

9.5) What are the disadvantages of cold drawn shafts?

Ans) The tolerance on the diameter and straightness are not very close compared with shafts produced by turning and grinding.

9.6) What are the various stresses induced on shafts?

Ans) The various stresses induced on shafts are shear stress, bending stress and torsional stress.

9.7) What are the various stress theories that can be applied to shafts?

Ans) The stress theories that can be applied to shafts are

Maximum principle stress theory

Maximum shear stress theory



Machine Design


9.8) What is jackshaft?

Ans) A jackshaft is an auxiliary or intermediate shaft between two shafts that are used in transmission of power. Its function is same as that of countershaft.

9.9) What is line shaft?

Ans) A line shaft consists of number of shafts connected in axial direction by means of couplings on which pulleys are mounted to drive a number of machines simultaneously by using a single electric motor.

9.10) What are the materials for making transmission shaft?

Ans) Transmission shafts are made of medium carbon steel (30C8, 40C8), high carbon steel (45C8, 50C8) and alloy steels which include nickel, nickel chromium and molybdenum steels.

9.11) How are commercial shafts made?

Ans) Commercial shafts are made by hot rolling, finished to size by cold drawing or by turning and grinding.

9.12) What are the disadvantages of cold drawn shafts?

Ans) The disadvantages are that the tolerances on their diameter and straightness are not very finished as in grinding and turning. Also residual stresses are produced at and near the surface of the shaft causing distortion.

9.13) What types of stresses are induced in shafts?

Ans) Axial stress, bearing stress (due to force acting upon mechanical elements), torsional stress (twisting forces on shaft) and linear stress (stress pushing shaft in linear direction).

9.14) Which theories of failure are applicable for shafts? Why?

Ans) The theories are

Maximum Principal Stress theory-since the shaft is subjected to bending and torsional moments without axial force and this theory holds good for brittle materials.

Maximum Shear stress theory- this is applicable to ductile materials.



Machine Design


9.15) Why is maximum principal stress theory not applicable to shafts?

Ans) Shafts are made of ductile materials and that is why this theory is not applicable.

9.16) Why is maximum shear stress theory used for shafts?

Ans) This theory holds good for only ductile materials of which shafts are made.

9.17) Define equivalent torsional moment and equivalent bending moment. State when these two terms are used in design of shafts.

Ans) Equivalent torsional moment- defined as the torsional moment, which when acting alone produces the same torsional shear stress in the shaft as under the combined action of bending and torsional moment. Shafts are design by this concept on basis of max shear stress theory.

Equivalent bending moment- defined as the bending moment which when acting alone will produce the same bending stresses as under the combined action of bending and torsional moment.

9.18) When a shaft is subjected to fluctuating loads, what will be the equivalent torsional moment and equivalent bending moment?

Ans) Under fluctuating loads the equivalent torsional moment will be

And the equivalent bending moment is ] where

and are shock and fatigue factors.

9.19) What do you understand by torsional rigidity?

Ans) Torsional rigidity is the property of the material if it does not twist too much under the action of external torque.

9.20) What do you understand by lateral rigidity?

Ans) Lateral rigidity is the property of the material if it does not deflect too much under the action of external forces and bending moment.

9.21) What is the permissible angle of twist for line shafts?

Ans) The permissible angle for line shafts is 3ᵒ per meter length.



Machine Design


9.22) How will you design shaft on basis of torsional rigidity?

Ans) Shafts are designed as per the permissible angle of twist per meter length which is on the basis of torsional rigidity.

9.23) What is the permissible shear stress as per ASME code?

Ans) The permissible shear stress is taken as 30% of the yield strength in tensile or 18% of the ultimate tensile strength.

9.24) How will you design shafts as per ASME Codes?

Ans) Shafts are designed as per ASME codes which are based on maximum shear stress theory of failure. The permissible shear stress is calculated by multiplying shock and fatigue factors to bending and torsional moments.

9.25) What are the advantages of hollow shaft over solid shaft?

Ans) Advantages of hollow shaft are as follows- more stiffness, more strength and higher natural frequency with same weight.

9.26) What are the disadvantages of hollow shafts over solid shafts?

Ans) The disadvantages are- costlier than solid shaft and requires more space as diameter is larger than that of solid shafts.

9.27) Explain the statement “A hollow shaft has greater strength and stiffness than solid shaft of equal weight”

Ans) The bending stresses and torsional shear stresses are zero at the center and maximum at the circumference and in hollow shafts the material at the center is removed and spread at large radius so that the outer fibers are more effective in resisting the applied moments. This explains the above statement.

9.48) Why is taper given to key? Why is taper given only on one side?

Ans) The taper is provided due to (1) when the key is inserted in the keyways of the shaft and the hub and pressed by means of hammer. It becomes tight due to wedge action. This insures tightness of joint in operating conditions and prevents loosening of the parts (2) due to taper, it is easy to remove the key and dismantle the joint. The taper of the key is on one side. Machining taper on two sides of key is more difficult than making taper on one side. Also, there is no specific advantage of taper on two sides.



Machine Design


9.49) What is Gib-head taper sunk key? What is its advantage?

Ans) The gib-head taper key is a normal taper key with gib-head. The tapered key is often provided with gib-head to facilitate removal.

9.50) What are the advantages and disadvantages of taper key over parallel key?

Ans) As compared with parallel key, taper key has the following advantages. (1)The taper surface results in wedge action and increases frictional force and the tightness of the joint. (2)The taper surface facilitates easy removal of the key, particularly with gib-head. The disadvantage is that machining taper on the surface increases cost.

9.51) What is the standard taper for sunk key?

Ans) The standard taper is 1 in 100.

9.52) What is feather key? Give its applications.

Ans) A feather key is a parallel key which is fixed either to the shaft or to the hub and which permits relative axial movement between them. Father keys are used where the parts mounted on the shaft are required to slide along the shaft such as clutches or gear shifting devices.

9.53) What are the advantages and disadvantages of feather key over flat key?

Ans) The advantages are. (1)There is a clearance fit between the key and the keyway in the hub. Therefore, the hub is free to slide over the key. (2)At the same time, there is no relative rotational movement between the shaft and the hub. Therefore, the feather key transmits the torque and at the same time permits some axial movement of the hub.

9.54) What is Woodruff key? Give its applications.

Ans) A Woodruff key is a sunk key in a form of an almost semicircular disk of uniform thickness. These keys are used on tapered shafts in machine tools and automobiles.

9.55) What are the advantages and disadvantages of Woodruff key over flat key?

Ans) The advantages of Woodruff key are as follows. (1) The Wood ruff key can be used on tapered shafts because it can align by slight rotation in the seat. (2) The



Machine Design


slight depth of key in the shaft prevents its tendency to slip over the shaft. The disadvantages of Woodruff key are as follows. (1) The extra depth of keyway in the shaft increases stress concentration and reduces its strength. (2) The key does not permit axial movement between the shaft and the hub.

9.56) What are the types of failure in flat key?

Ans) Failure due to shear stress and failure due to compressive stress are the types of failure in flat key.

9.57) What are the two types of stresses in flat key?

Ans) Shear stress and compressive stress are the two types of stresses in flat key.

9.58) What is Kennedy key? Give its applications.

Ans) The Kennedy consists of two square keys. Kennedy key is used for heavy duty applications.

9.59) What are the advantages and disadvantages of Kennedy key over flat key?

Ans) Since there are two keys, the torque transmitted by each key is one half of the total torque. This is an advantage over a single flat key.

9.60) What are splines? Where do you use them?

Ans) Splines are keys which are made integral with the shaft. They are used when there is a relative axial motion between the shaft and the hub. Splines are cut on the shaft by milling and on the hub by broaching.

9.61) What is the difference between splines and keys?

Ans) Splines are keys which are made integral with the shaft whereas keys are altogether different component.

9.62) What are the types of spline?

Ans) The different types of splines are straight sided splines, involute splines and serrations.

9.63) What are the advantages and disadvantages of involute splines over straight-sided splines?



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Ans) The advantages are (1) Greater strength relative to their size. (2) Involute splines are self centering and tend to adjust to an even distribution of load. The disadvantage is that the cost of involute splines is more than straight sided splines.

9.64) What is coupling? Where do you use it?

Ans) A coupling can be defined as a mechanical device that permanently joins two rotating shafts to each other. The most common application of coupling is joining of shafts of two separately built or purchased units so that a new machine can be formed.

9.65) What is the difference between a clutch and coupling?

Ans) Coupling is a permanent connection, while the clutch can connect or disconnect two shafts at the will of the operator.

9.66) What is the difference between rigid and flexible couplings?

Ans) While the flexible coupling is capable of tolerating a small amount of misalignment between the shafts, there is no such provision in rigid coupling.

9.67) Why are flexible couplings popular?

Ans) In practice, misalignment always exists due to imperfect workmanship. Therefore, flexible couplings are more popular.

9.68) What are the requirements of a good coupling?

Ans) 1. Should be able to transmit torque from driving shaft to driven shaft

2. Should keep two shafts in proper alignment.

3. Should be easy to assemble and disassemble

9.69) Give practical applications of couplings.

Ans) A coupling is used to join the output shaft of an engine to the input shaft of a pump to raise water from well

9.70) What is Muff coupling?

Ans) It is also known as sleeve coupling or box coupling.

It is a type of rigid coupling.



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9.71) What are the advantages and disadvantages of Muff coupling?

Ans) Advantages

It is simple to design and manufacture.

It has no projecting parts except the key head.

It has compact construction with small radial dimensions.

Disadvantages

It is difficult to assemble and disassemble

Rigid type require accurate alignment of shafts

Cannot absorb shocks and vibrations

9.72) What is a clamp coupling?

Ans) Also known as compression coupling or split muff coupling

The sleeve is made of two halves that are split along a plane passing through the axis of the shaft.

9.73) What are advantages and disadvantages of clamp coupling?

Ans) Easy to assemble and disassemble

Small diametrical dimensions

Difficulty in dy A: namic balancing of the coupling.

Unsuitable for shock loads.

9.74) How does the working of clamp coupling differ from that of muff coupling?

Ans) In muff coupling the torque is transmitted by shear resistance of keys.

On the other hand the torque is transmitted partly by means of friction between the sleeve halves and the shaft partly by shear resistance of key.

9.75) What is the construction of rigid flange coupling?

Ans) It consists of two flanges, one keyed to the driving shaft and other to the driving shaft.

The two flanges are connected together by means of four or six bolts arranged on a circle concentric with the axis of the shaft.



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9.76) What is the purpose of spigot and recess in rigid flanged coupling?

Ans) Since it is a rigid type of coupling, provision should be made for precise location of the axes of the two shafts.

9.77) What is the difference between protected and unprotected rigid flanged coupling?

Ans) The revolving bolt heads and nuts are dangerous to the operator in unprotected type, whereas circumferential rims cover the heads of bolts & nuts.

9.78) What are the advantages and disadvantages of rigid flanged coupling?

Ans) Advantages

High torque transmitting capacity

Easy to assemble & disassemble

Disadvantages

Cannot tolerate misalignment between axis of two shafts

Can be used where motion is free of shocks 7& vibrations

9.79) Not applicable

9.80) In what situation flexible coupling is used?

Ans) It is used when the two shafts are not properly aligned

When the shafts are subjected to expansion & contraction

9.81) What is the construction of bushed pin flexible coupling?

Ans) It consists of two flanges, one keyed to the input shaft and other to the output shaft.

9.82) What is the purpose of rubber bush in bushed pin flexible coupling?

Ans) It accommodates for misalignment & absorbs shocks and vibrations.

9.83) What are the causes of misalignment between two connecting shafts?

Ans) Deflection of shafts due to lateral forces, error in shaft mounting, thermal expansion of parts.



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9.84) What are the types of misalignment between two connecting shafts?

Ans) Lateral misalignment, axial misalignment, angular misalignment.

9.85) What are advantages & disadvantages of bushed pin flexible coupling?

Ans) Can tolerate 0.5mm lateral or axial, 1.5 degrees of angular misalignment, high torque transmission.

High cost, require more radial space.

9.86) In bushed flexible coupling why is there a clearance between flanges?

Ans) It is essential for taking care of angular misalignment between two shafts.

9.87) For connecting shafts of a particular diameter bushed pin type coupling either has greater no of bolts or larger bolt diameter than rigid coupling. Why?

Ans) Because it reduces force acting on the bolts and lowers bearing pressure on the rubber bush.

9.88) ‘The most satisfactory location of coupling is one that is very close to bearing on shaft’. Why?

Ans) The shaft Does not fail instantaneously.It avoids accident.

9.89) Where do you design the shafts on the basis of lateral rigidity?

Ans) A Component is considered as rigid when it doesn’t deflect or bend too much due to external forces or moments.

9.90) What is the permissible deflection for transmission shafts?

Ans) delta=(0.001)L to (0.003)L.

9.91) What is the Permissible shaft deflection at the gears?

Ans) Delta=(0.01)m.

9.92) What are the methods of improving lateral rigidity of shafts?

Ans) Methods of improving lateral rigidity are:-



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1) reduce the span length.

2) increase the number of supports.

3) reduce the number of joints.

4) assemble the components with pre-Load.

5) Lubricate the contact surfaces wuth high viscosity oil.

9.93) ’It is not advisable to use expensive alloy steels in place of plain carbon steels where lateral rigidity is the design criterion’.Why?

Ans) The modulus of elasticity is practically same for all types of steel,whether plain carbon steel or alloy steel.

9.94) What are the methods of determining the lateral deflection of shaft?

Ans) Methods are:-1)double integration method.

2)area moment method.

3)strain energy method.

4)graphical integration method.

9.95) State Castigliano’s theorem. Where do you use it?

Ans) The theorem states that:-“when a body elastically deflected by any combination of forces or moments ,the deflection at any direction is equal to the partial derivative of total strain energy of the body with respect to a force located at that point and acting in that direction.

9.96) Explain the principle of area moment method.

Ans) The basic principle of this method is stated as’The vertical distance of any point C on the elastic curve of the shaft,from the tangent at any other point A on the elastic curve,is equal to the moment of area of (M/EI) diagram between A & C with respect to the ordinate through C.’

9.98) What is the critical speed of shaft?

Ans) The critical speed of the shaft is the speed at which the rotating shaft becomes dynamically unstable and starts vibrate violently in transverse direction.

9.99) What are the first and second critical speeds of shaft?



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Ans) The shaft supported between two end bearings and having two attached masses is considered. First critical method:- Masses are not perpendicular to the axis. Second critical method:- Masses are perpendicular to the axis.

9.100) How is resonance avoided in shafts?

Ans) Resonance can be avoided by two methods:-

1)In Some applications ,shafts are made very rigid with very high critical speed (ncr),which is far away from running speed(n).In this case,the shaft never reaches the critical speed and no resonance occurs.

2)There are applications where shafts are made very slender with very low critical speed (ncr)The running sped (n) is two to three times of the critical speed.In this case,the shaft passes quickly through the critical speed and no damage is done.The shaft never reaches the critical speed during operating conditions and no resonance occurs.

Ch.10- Design of Springs

10.1) What is Spring?



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Ans) A Spring is defined as an elastic machine element that deflects under the action of the load and returns to its original shape when the load is removed.

10.2) What are the functions of spring?

Ans) Functions of the spring are:-

1)Used to absorb shocks and vibrations.

2)used to store energy.

3)used to measure the force.

4)used to apply force and control motion.

10.3) What are the applications of spring?

Ans) Vehicle suspension springs, railway buffer springs, buffer springs elevator and vibration mounts for machinery, springs used in locks,toys,movie-camers,circuit breakers and starters etc.

10.4) What are the types of springs?

Ans) Helical springs, compression spring, extension spring, Semi-elliptic Leaf spring.

10.5) What type of stress is induced in Helical compression spring?

Ans) Torsional shear stress is induced in the helical compression spring.

10.6) What type of stress is induced in helical extension spring?

Ans) Torsional shear stress is induced in the helical extension spring.

10.7) Distinguish between closely coiled and open coiled Helical springs?

Closely Coiled Helical Spring Open Coiled Helical Spring

1)Spring wire is coiled so 1)Spring wire is coiled at



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10.8) What are the advantages of helical springs?

Ans) The advantages of helical springs are:

i) They are easy to manufacture.

ii) They are cheaper than other types of springs.

iii) Their reliability is high.

iv) The deflection of the spring is linearly proportional to the force acting on the spring.

10.9) What is helical torsion spring? How does it differ from compression spring?

Ans) The helical torsion spring is similar to that of compression or extension spring except that the ends are formed in such a way that the spring is loaded by a torque about the axis of coils.

10.10) What type of stress is induced in helical torsion spring?

Ans) Bending stresses is induced in helical torsion spring.

10.11) Explain the construction of multi-leaf spring.

Ans) A multi-spring or laminated spring consists of a series of flat plates, usually of semi-elliptical shape. The flat plates, called leaves, have varying lengths. The leaves are held together by means of U-bolts and a centre clip. The longest leaf, called the master leaf, is bent at the two ends to form spring eyes.

10.12) What are the applications of multi-leaf spring?

Ans) Multi-leaf springs are widely used in automobile and railroad suspension.

10.13) What is a spring index?

Ans) The spring index is defined as the ratio of mean coil diameter to wire diameter.

large

closed distance

2)Helix angle is small 2)Helix Angle is large

3)It is usually less than 10°. 3)More than 10°.



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10.14) What is free length of helical compression spring?

Ans) Free length is defined as the axial length of an unloaded helical compression spring.

10.15) What is compressed length of helical compression spring?

Ans) Compressed length is defined as the axial length of the spring, which is subjected to maximum compressive force.

10.16) What is solid length of helical compression spring?

Ans) Solid length is defined as the axial length of the spring which is so compressed that the adjacent coils touch each other.

10.17) What is stiffness of spring?

Ans) The stiffness of the spring (k) is defined as the force required to produce unit deflection.

10.18) What are active coils of spring?

Ans) Active coils are the coils in the spring which contribute to spring action, support the external force and deflect under the action of force.

10.19) What are inactive coils of spring?

Ans) Inactive coils is a portion of the end coils, which is in contact with the seat, does not contribute to spring action.

10.20) State the relationship between active, inactive and total number of coils in the helical compression spring.

Ans) Number of inactive coils=Total number of coils – Number of active coils

= Nt - N

10.21) What are the four different styles of end for helical compression spring?

Ans) The four different styles of end for helical compression springs are:

(a)Plain ends. (b)Plain and ground ends.

(c)Square ends. (d)Square and ground ends



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10.22) What are the different styles of end for helical extension spring?

Ans) The different styles of end for helical extension springs are:

(a)V-hook. (b)Rectangular hook.

(c)Full hook. (d)Extended hook.

10.23) State the relationship between active coils and total number of coils in the helical extension spring.

Ans) The number of active coils (N) is same as the number of coils (Nt).

i.e. N = Nt

10.24) What types of shear stresses are induced in the wire of helical spring?

Ans) Direct or transverse shear stress, Torsional shear stress and Stress due to curvature of coil.

10.25) Sketch the distribution of shear stresses in the wire of helical spring?

Ans) not done…..

10.26) What is Wahl factor? Why is it used?

Ans) The Wahl factor (K) provides a simple method to find out resultant stresses in the spring.

+

10.27) Write down load-deflection equation for helical spring.

Ans)

Where P : Axial force.

D : Mean diameter of coil.

N : Number of active coils.

G : Modulus of rigidity.

D : Wire diameter.



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10.28) Write down the expression for strain energy stored in helical spring.

Ans) U= 4P2D3N / Gd4

where

P= Axial Force

G= Modulus of Rigidity

D= Mean coil diameter

d= Wire diameter

N= Number of active coils

10.29) What are the objectives of series and parallel connections of springs?

Ans) The objectives of series and parallel connections of springs are: To save the space, to change the stiffness of the system at a certain deflection and to provide a fail-safe system.

10.30) Two springs of stiffness k1 and k2 are connected in series. What is the stiffness of connection?

Ans) 1/k= 1/k1 + 1/k2 +…

where k is the stiffness of the combination and k1, k2 … are the stiffness of individual springs.

10.31) Two springs of stiffness k1 and k2 are connected in parallel. What is the stiffness of connection

Ans) k= k1 + k2 +…

where k is the stiffness of the combination and k1, k2 … are the stiffness of individual springs.

10.32) What are the four basic varieties of steel wires used for making helical spring?

Ans) (i) patented and cold-drawn steel wires (unalloyed);

(ii) oil-hardened and tempered spring steel wires and valve spring wires (unalloyed);

(iii) oil-hardened and tempered steel wires (alloyed); and

(iv)stainless steel spring wires for normal corrosion resistance.



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10.33) Where do you use patented and cold drawn steel wire springs?

Ans) The patented and cold drawn steel wires are used in springs subjected to static forces and are classified into Grade 1 (low load cycles), Grade 2 (moderate load cycles), Grade 3 (moderate dynamic loads) and Grade 4 (severe stresses).

10.34) Where do you use oil-hardened and tempered steel wire springs?

Ans) The alloyed varieties of oil-hardened and tempered steel wire springs are used for elevated temperature applications.

10.35) ‘Permissible torsional shear stress is 30% of ultimate tensile strength of spring wire.’ Why?

Ans) For springs subjected to static load,

Permissible torsional shear stress= Torsional yield strength / 1.5

Taking Torsional yield strength= 0.577 x Tensile yield strength

And Tensile yield strength= 0.75 x Ultimate tensile strength

We get Permissible torsional shear stress= 0.577 x 0.75 x Ultimate tensile strength / 1.5

Hence, Permissible torsional shear stress= 0.3 x ultimate tensile strength

10.36) How will you design buckle-proof spring?

Ans) For designing buckle-proof spring, the ratio of free length to mean coil diameter should be less than 2.6. However if the ratio cannot be restricted below 2.6, then the coil will have to be guided in a sleeve or over an arbor to prevent buckling.

10.37) What is pulsating shear stress? Why are springs subjected to pulsating shear stress?

Ans) Pulsating shear stress is the stress undergone by the spring, changing its load magnitude from compression to tension and varying from zero to shear endurance limit. Springs are subjected to fluctuating stresses on the basis of two criteria- design for infinite life and design for finite life.

10.38) Explain fatigue diagram for spring design.

Ans) The fatigue diagram for spring design shows the different criterion of failures. The torsional shear stress, yield strength and ultimate tensile strength are calculated with appropriate formulae and the equations are used in design of springs.



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10.39) What is surge in spring?

Ans) When there are impact loads on the springs, the stress propagates along the spring wire. The end coil of the spring in contact with the applied load takes up whole of the deflection and then it transmits a large part of its deflection to the adjacent coils. This wave of compression travels along the spring indefinitely. This results in very large deflections and correspondingly very high stresses. Under these conditions, it is possible that the spring may fail. This phenomenon is called surge.

10.40) How will you avoid surge in spring?

Ans) (i) By using friction dampers on the centre coils so that the wave propagation dies out.

(ii) By using springs of natural high frequency.

(iii) By using springs having pitch of the coils near the ends different than at the centre to have different natural frequencies.

10.41) What is concentric spring?

Ans) A concentric spring is a composite or cluster spring in which two or more than two coiled helical springs are placed- one inside the other.

10.42) What are the advantages of concentric spring?

Ans) (i) To obtain greater spring force within a given space.

(ii) To ensure the operation of mechanism in the event of failure of one of the springs.

10.43) What are the applications of concentric spring?

Ans) Concentric springs are used in automobile clutches, valve springs in aircraft, heavy duty diesel engines and rail-road car suspension systems.

10.44) What is spiral spring?

Ans) A spiral spring is formed from a flat strip or wire wound in the form of a spiral, loaded by torque about an axis normal to the plane of the spiral.

10.45) What are the advantages of spiral spring?



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Ans) Strain energy, stored in spirals, is utilized in any useful way when the spirals open out slowly.

10.46) What are the applications of spiral spring?

Ans) Spiral springs are used in watches and gramophones.

10.47) What are graduated-length and full-length leaves in multi-leaf spring?

Ans) A multi-leaf spring has leaves of graduated length. The leaf at the top has maximum length, called master leaf and the length gradually decreases from the top leaf to the bottom leaf. One or two full-length leaves are stacked between the master leaf and graduated-length leaves to support the transverse shear force.

10.48) What are the materials used for making leaves of a multi-leaf spring?

Ans) The material used for making leaves of a multi-leaf spring is steel

(55Si2Mn90,50Crl or 50CrlV23)

10.49) What is nip of a leaf spring?

Ans) The initial gap between the extra full length leaf and the graduated- length leaf before the assembly, is called nip.

10.50) What is the objective of nipping of leaf spring?

Ans) Nipping is used for equalizing the stress in different leaves by pre stressing the leaves.

10:51) What is Belleville (coned disk) spring?

Ans) Belleville spring is a coned shaped spring, which has got typical load deflection characteristics.

10.52) What are the advantages of Belleville Spring?

Ans) # Simple in construction & easy to manufacture.

# Useful for large forces and small spring deflection.

# It provides a wide range of spring constant & making it versatile.



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10.53) What are the applications of Belleville Spring?

Ans) Belleville spring are used an plate clutch & brakes, gun recoil mechanism, relief valves and in variety of bolted connections.

10.54) What is shot peeing of spring?

Ans) Shot peeing is a method of creating a layer of residual compressive stress is induced in the surface of the spring wire and hence reducing the chance of crack prorogation.

10.55) What is the objective of shot peeing of spring?

Ans) Shot peeing is used for preventing spring wire from fatigue crack.

Ch.11 – Design of Clutch

11.1) What is a clutch?



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Ans) The clutch is a mechanical device, that is used to connect or disconnect the source of power from the remaining parts of the power transmission system.It can be stated, “as a mechanism which enables the rotary motion of one shaft to be transmitted, when desired to a second shaft the axis of which is coincident with that of the first.”

11.2) What is the difference between clutch and flange coupling?

Ans) The basic difference between coupling and clutch is that a coupling is used for permanent connections(i.e.driving and driven shafts are permanently connected by coupling and it is not possible to disconnect the shafts,unless dismantled).Whereas,clutch can connect or disconnect the two shafts as and when required.

11.3) What is the difference between a clutch and brake?

Ans) The difference can be made on the basis of initial and final working conditions.In a clutch the driving member is rotating initially and driven member is at rest,but at final condition both are at rest.In brakes initially the brake drum is rotating and shoe is at rest and at final conditions both comes to rest.

11.4) Where do you use clutch?

Ans) The clutch is required to transmit given power.The power transmitted by the clutch is product of torque and speed,therefore greater the speed,lower is the torque to be transmitted,therefore clutch should be placed at high speed side(i.e.between the engine and the gear-box).

11.5) What is the function of an automotive clutch?

Ans) Automotive clutch consists of a “clutch delay valve” which operates on the principle that engagement needs to occur at a certain rate to be efficient and that engaging at quicker rate could damage the drive train components.CDVs operates as a one-way restrictor valves that limit the volume of fluid that can move through the lines in a given time.

11.6) Specify the types of clutch?

Ans) Clutches are classified into following groups:

(i)Positive Contact Clutches. (ii)Friction Clutches.



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(iii)Electromagnetic Clutches. (iv)Fluid Clutches and Couplings.

11.7) Name the different types of clutches.Give one practical application of each.

Ans) (i)Positive Clutch.(used in some machine tools). (ii)Friction Clutch.(used in automobiles,textile machines) (iii)Electromagnetic Clutch (used for coupling and un-coupling power or sensing device). (iv)Fluid Clutch (used in cars,trucks,buses).

11.8) What is positive clutch?

Ans) A clutch that consists of two mating surfaces with interconnecting elements,such as teeth,that lock together during engagement to prevent slipping.They are also known as “mechanical lockup clutches”.

11.9) Why a positive clutch is used?

Ans) A positive clutch is used because there in no slipping takes place and since there are no friction members,heat is not generated and hence use of coolant is eliminated,also they can transmit large amount of torque.

11.10) By what means power is transmitted by clutches?

Ans) In friction clutch the power is transmitted by means of frictional force between the driving and driven flanges.In positive clutch it is achieved by the inter-locking of jaws or teeth.In electromagnetic clutch it is achieved by means of the magnetic field.Whereas,in fluid clutch power is transmitted by means of hydraulic pressure.

11.11) What factors should be considered in designing friction clutch?

Ans) Following factors should be considered:

(i)Selection of proper type of clutch that is suitable for the application. (ii)Selection of suitable friction material at the contact surface. (iii)Designing the clutch for sufficient torque capacity. (iv)Engagement and disengagement should be without shock or jerk. (v)Provision for holding the contacting surfaces together by clutch itself and without any external assistance. (vi)Low weight for rotating parts to reduce inertia forces, particularly in high-speed applications.



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(vii)Provision for taking or compensating wear of rubbing surfaces. (viii)Provision for carrying away the heat generated at the rubbing surfaces.

11.11a) Why splines are used in mechanical clutches?

Ans) Splines are used in mechanical clutches as a means for connecting the pair of disks to the driven shaft, so that they are free to move in an axial direction on the splined sleeve.

11.12) What are the advantages of single-plate clutch over multi-plate clutch?

Ans) (i)Single-plate clutch have a higher co-efficient of friction as compared to multi-plate clutch.

(ii)Torque capacity of single-plate clutch is high compared to multi-plate of same dimension.

11.13) What are the advantages of multi-plate clutch over single-plate clutch?

Ans) (i)The construction of multi-plate clutch is compact as compared to single-plate clutch. (ii)The torque transmitting capacity is more in multi-plate clutch as compared to single-plate clutch.

11.14) What are the two theories applied to friction plates?

Ans) The theories applied to friction plates are listed below:

(i)Uniform pressure theory. (ii)Uniform wear theory.

11.15) What is the assumption of uniform pressure theory?

Ans) It is assumed in the theory that in case of new clutches employing a number of springs, the pressure remains constant over the entire surface area of the friction disk(i.e. ‘p’ is assumed to be constant).

11.16) What is the assumption of uniform wear theory?

Ans) According to this theory, it is assumed that the wear is uniformly distributed over the entire surface area of the friction disk. But this assumption is used for worn-out clutches.(i.e.pr=const).



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11.17) Why clutches are designed on the basis of uniform wear?

Ans) In case of a new clutch the intensity of pressure is uniform along the surface but in case of old or worn out clutch uniform wear theory is more accurate. A clutch designed using wear theory gives a safer design and hence is commonly used.

11.18) What are the phases of wear mechanism in friction lining?

Ans) There are two phases of wear mechanism in friction lining: (i)When the lining is new, uniform pressure theory is applicable(p=const),since the wear at the outer radius will be more and will release the pressure at the outer edge. (ii)Since the pressure is released there will be no further wear at the outer edge. The wear will now take place at the inner edge due to contact of the pressure plate. This will release pressure and stop further wear at the inner edge. This action goes on till ‘pr’ becomes constant.

11.20) Where do you use single-plate clutch?

Ans) Single-plate clutches are used in applications where large radial space is available, such as trucks and cars.

11.21) Where do you use multi-plate clutch?

Ans) We use multi-plate clutch where compact construction is required and high torque is to be transmitted.

11.22) In case of multi-plate clutch if (n1)is number of disks on driving shaft and (n2) is the number of disks on driven shaft, then what is the number of pairs of contacting surfaces?

Ans) We know that ,

Number of disks = (number of pairs of contacting surfaces + 1)

= (n+1) ................................................(a)

Let, n1=number of disks on driving shaft.

n2=number of disks on driven shaft.

Substituting in (a)

n1+n2=number of pairs of contacting surfaces + 1

OR

number of pairs of contacting surfaces= n1 + n2 -1



Machine Design


11.23) Why is heat dissipation necessary in clutches?

Ans) Heat dissipation necessary in clutches to reduce the wear rate.

11.24) Give practical applications of single plate clutch?

Ans) The practical applications of single plate clutch is where large radial space is available, such as trucks & cars.

11.25) Give practical applications of multi-plate clutch?

Ans) The practical applications of multi-plate clutch is where compact construction is desirable such as scooter & motor cycle.

11.26) Distinguish between dry and wet operations of clutch

Ans) i) Dry clutch has higher coefficient of friction. In wet clutches the coeffient of friction is reduced due to oil.

ii) The torque capacity of dry clutch is high compared with torque capacity of of wet clutch of same dimensions.

iii) Heat dissipation is more difficult in dry clutches. In wet clutches,the lubricating oil carries away the frictional heat.

iv) The engagement in wet clutch is smoother than in case of dry clutch.

11.27) Name the friction materials used in clutches and brakes?

Ans) The frition materials used in clutches and brakes are:

For light load and low speed → wood, cork & leather.

For heavy load and high speed → asbestos based & sintered metals.

11.28) What is woven asbestos friction material?

Ans) A woven asbestos friction disk consists of asbestos fibre woven around brass, copper or zinc wires and impregnated with rubber or asphalt. They have an endless circular weave, that increases the centrifugal bursting strength.

11.29) What is moulded asbestos friction material?



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Ans) Moulded asbestos friction disks are prepared from the wet mixture of brass chips & asbestos, that is poured into the mould & given the shape of the disk. The mixture is then heated & pressed for a specific curing time.

11.30) Compare woven and moulded asbestos friction materials.

Ans) The difference between woven and moulded asbestos materials is as follows:

i) Woven material is flexible, while moulded asbestos is rigid.

ii) Woven material has higher coefficient of friction.

iii) Woven material conforms more readily to clutch surface while moulded materials takes longer to wear in the seat.

11.31) What are the drawbacks of asbestos friction materials?

Ans) The drawbacks of asbestos friction material is that it is subjected to destruction by heat at comparatively low temperature.

11.32) What are the advantages of sintered metal friction materials over asbestos friction materials?

Ans) The advantages of sintered metal friction materials over asbestos friction materials are as follows:

i) They have higher wear resistance.

ii) They can be used at high temperatures.

iii) The coefficient of friction is constant over a wide range of temperature and pressure.

iv) They are unaffected by environmental conditions, such as dampness, salt water or fungi.

11.33) Why are asbestos friction materials prohibited in number of countries?

Ans) It has been found that when asbestos dust is inhaled, it leads to cancer. The body cells, which come in contact with asbestos particles, are agitated and developed into cancer cells. Lung cancer is common among operators working in the atmosphere of asbestos dust. There are federal regulations in number of countries, that prohibit the use of asbestos in clutch and brakes linings.

11.34) What are the four ingredients of modern friction lining?



Machine Design


Ans) The four ingredients of modern friction lining are fibres, filler, binder and friction modifiers.

11.35) What is the recommended semi cone angle of cone clutch?

Ans) The recommended semi cone angle of cone clutch is 12.50.

11.36) Why is semi-cone angle of cone clutch 12.50?

Ans) The conical surface results in considerable friction force even witha small engaging force due to wedge action. Therefore semi-cone angle of cone clutch is 12.50.

11.37) What are the advantages of cone clutch?

Ans) The advantages of cone clutch is that it is simple in construction & easy to disengage.

11.38) What are the drawback of cone clutch?

Ans) The main drawback is the strict requirement for the coaxiality of two shafts.

11.39) Give practical application of cone clutch.

Ans) The practical application of cone clutch is in electric motors.

11.40) The coefficient of friction between the contacting surfaces of a cone clutch is 0.2. What is the minimum value of semi-cone angle?

Ans) To avoid self engagement and to facilitate disengagement.

α (semi-cone angle) >ø (angle of static friction)

Given:µ = 0.2

α > tan-1(0.2)

α > 11.30

11.41) What are the advantages of centrifugal clutch?

Ans) Advantage of centrifugal clutch are:

1)The centrifugal clutches permit the drive motor or engine to start, warm up and accelerate to the operating speed without load.



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2)Engagement of centrifugal clutch is very smooth

11.42) What are the drawbacks of centrifugal clutch?

11.43) Give examples of centrifugal clutch.

11.44) Plot a graph of temperature of clutch assembly against time.

11.45) What are the factors on which the coefficient of friction between contacting

surfaces depends?

11.46) Why a service factor is used for calculating the design capacity of a clutch?

Ans) In most of the cases, the accelerating or starting torque of the machine is much more than the running torque. If the clutch is not designed for this increased torque it will slip under the load and no power can be transmitted. There is another factor to account for additional torque. In many applications, the torque developed for the prime mover fluctuates and also, the torque requirement by driven machinery fluctuates as in the case of presses.This two factor are accounted by means of service factor.

Ch.12 – Design of Brake



Machine Design


12.1) What is a brake?

Ans) A brake is defined as a mechanical device which is used to absorb the energy possessed by a moving system or mechanism by means of friction.

12.2) What is the function of brake?

Ans) The function of the brake is to slow down or completely stop the motion of a moving system, such as a rotating drum, machine or vehicle.

12.3) State different types of brakes and give atleast one practical application of each.

Ans) The different types of brakes are:

1)Mechanical brakes. It is used in roller coaster.

2)Hydraulic and pneumatic brakes. It is used in cars and other automobiles.

3)Electrical brakes. It is used in reversible hydropower plants.

12.4) What is block brake with short shoe? Where do use it?

Ans) A block brake with short shoe consist of a simple block, which is pressed against the rotating drum by means of a lever. The friction between the block and the brake drum causes the retardation of the drum. This type of brake commonly employed in railway trains.

12.5) What is the disadvantage of block brake with one short shoe? What is the remedy?

Ans) The main disadvantage with one short shoe is the tendency of the brake drum shaft to bend under the action of normal reaction. The remedy is to use two symmetrical blocks at the opposite sides of the brake drum.

12.6) What is self-locking brake?

Ans) When no external force is required for braking action. Such a brake is called self- locking brake

12.7) What is the condition of self-locking block brake?

Ans) We know that the braking force P={(a-xc)/b}*N. For self-locking (a=xc)

12.8) What is partially self-energizing block brake?

Ans) When the moment due to braking effort and moment due to friction force are both anticlockwise. Such a brake is called a partially self-energizing brake.



Machine Design


12.9) What is the advantage of pivoted shoe brake over fixed shoe brake?

Ans) In case of pivoted shoe brake, the location of the pivot can be selected in such a way that the moment of the frictional force about the pivot is zero. This is the main advantage of pivoted shoe brake.

12.10) What is internal expanding shoe brake? Where do you use it?

Ans) Internal expanding shoe brake consist of a shoe, which is pivoted at one end and subjected to an actuating force on the other end. Friction lining is fixed on the shoe, lining and pivot is placed inside the brake drum. The actuating force is usually provided by means of a hydraulic cylinder or a cam mechanism. Internal expanding brake is used in vehicle, conveyor and hoist.

12.11) What are advantages of internal expanding shoe brake?

Ans) Advantages of internal expanding shoe brake are as follows:

1)It has simple construction with small number of parts.

2) It is cheaper compared with other brakes and also reliable.

3)It requires little maintenance.

4) It offers protection against entry of foreign particles.

12.12) What are disadvantages of internal expanding shoe brake?

Ans) The disadvantages of internal expanding shoe brake are as follows:

1)It has relatively poor heat dissipating capacity.

2)It becomes self-locking due to wear, if not properly designed.

12.13) What is differential band brake?

Ans) In Case of differential band brake, neither end of the band passes through the fulcrum of the actuating lever. Such brakes can be designed for the condition of self locking.

12.14) What is the condition of self locking differential band brake?Why should it be avoided in speed-control brakes?

Ans) Condition of self locking is given by,(a/b)<=e

The self locking property is undesirable in most of the applications of the brake, since the brake is out of the operators control. In such a situation no external



Machine Design


force is required to apply the brake. A band in contact with the drum automatically grabs and the operator cannot prevent it. Hence it should be avoided in speed-control brakes.

12.15) What is internal expanding shoe brake? Where do you use it?

Ans) An internal expanding brake consist of a shoe, that is pivoted at one end and other end is subjected to an actuating force , a friction lining is fixed on the shoe and the complete assembly of shoe, lining and pivot is placed inside the drum brake.

12.16) What are the advantages of internal expanding shoe brake?

Ans) Internal expanding brake offers following advantages:

It has simple construction with small number of parts hence it is cheaper than other types of brake.

It is more reliable due to small number of parts.

It requires little maintenance.

In internal expanding brakes even small actuating force can produce large braking torque.

12.17) What are disadvantages of internal expanding brake?

Ans) An internal expanding brake has relatively poor heat dissipating capacity and it becomes self-locking due to wear.

12.18) What is the magnitude of pedal force in case of automotive type internal expanding brake? Why?

Ans) The maximum force exerted with right foot for the fifth percentile female is 22N and for the male approximately 42N. Therefore from ergonomic consideration, the brake system should be designed for a maximum pedal force of 22 to 25N. with booster, the pedal force can be as low as 11 to 17N.

12.19) What is simple band brake?

Ans) When end of the steel band passes through the fulcrum of the actuating lever, the brake is called as the simple band brake.

12.20) What is differential band brake?

Ans) A differential brake, in which neither end of the steel band passes through the fulcrum of the actuating lever.



Machine Design


12.21) What is the condition of self-locking in differential band brake? Why should it be avoided in speed control brake?

Ans) For self-locking condition, the force P is equal to zero or negative, and in self-locking the brake is out of operator’s control hence self-locking is avoided in speed control brakes.

12.22) In which applications, self-locking differential band brakes are used?

Ans) Self-locking differential band brake is used in back-stop mechanism.

12.23) Distinguish between simple and differential band brakes?

Ans) The major difference between simple and differential band brake is that the position of steel band, in simple band brake one end of steel band passes through the fulcrum of actuating lever and in differential band brake neither end of steel band passé through the fulcrum.

12.24) What are the advantages of band brake?

Ans) Band brakes offers following advantages:

Band brake has simple construction. It has small number of parts. These features reduce the cost of band brake.

Band brake little maintenance.

Band brakes are more reliable due to small number of parts.

12.25) What are the disadvantages of band brakes?

Ans) The disadvantages of band brake are they have poor heat dissipation capacity and wear of friction lining is uneven from one end to other end.

12.26) What are the applications of band brake?

Ans) Band brakes are used in application like bucket conveyor, hoist and chain saw. They are more popular as back-stop devices.

12.27) What is back-stop band brake?

Ans) Aback-stop brake is a device that is used to prevent the reverse rotation of drum when such rotations are not required.



Machine Design


12.28) What is the effect of temperature rise at the braking surface?

Ans) When the temperature rises, the coefficient of friction decreases, adversely affecting the torque capacity of the brake. At high temperature , there is rapid wear of the friction lining, that reduces the life of the lining.

12.29) What is significance of (pv) factor? Where, p= intensity of normal pressure (N/mm2), v=rubbing speed (m/mim).

Ans) When the coefficient of friction is constant, the rate of heat generated is proportional to the product (pv). It is very difficult to precisely calculate temperature rise. In preliminary design analysis, very often the product pv is considered in place of temperature rise.

12.30) What is the relation between temperature rise of drum brake assembly, energy absorbed by brake , mass of brake drum assembly and its specific heat?

Ans) The relation is given by,

Δt=E/mc

12.31) What is the advantages disc brake over drum brake?

Ans) In disk brake the friction lining on the calliper contacts only a small portion of the rim, leaving the remaining portion to dissipate the heat to the surrounding. Where as in drum brake there is very less such area is available to dissipate the heat.

12.32) What is the specific advantage of differential band brake over other types of band brake?

Ans) Differential band brake are such design that can be designed for the condition of self-locking.

12.33) What are the factors upon which the braking capacity of brake depends?

Ans) Brake capacity depends upon the following five factors:

The unit pressure between braking surfaces.

The contacting area of braking surface.

The radius of the brake drum.

The coefficient of friction.



Machine Design


The ability of the brake to dissipate heat that is equivalent to the energy being absorbed.

12.34) Compare block and band brakes. State their relative advantages and disadvantages?

Ans) The main disadvantages of block brake is the tendency of the brake drum shaft to bend under the action of normal reaction and block brake have more numbers of parts which makes it costly whereas in band brake the tendency of shaft to bend is less and in band brake less number of parts required which makes it cheaper as compare to block brake.

12.35) What type of brake is used in passenger vehicles?

Ans) Internal expanding shoe brake and disk brake.

Ch.13 – Design of Belt Drives

13.1) Why are belt drives called flexible drives?



Machine Design


Ans) Belt drives are called flexible drives because there is an intermediate link (belt) between the driving and the driven shafts and thus link is flexible.

13.2) What are the three basic elements of a belt drive?

Ans) The three basic elements of a belt drive are the driving shaft, the driven shaft and an endless belt.

13.3) What are the types of belts?

Ans) The different types of belts are Flat belts, V-belts, Round belts, Leather belt & fabric rubber belt.

13.4) What are the advantages of flat-belt drive?

Ans) # Easy to maintain and cheap.

# Can be used in dusty and abrasive atmosphere.

# It can be used for long centre distance l-----in--------k up to 15m

# Design is simple and in-expensive.

13.5) What are the disadvantages of flat-belt drive?

Ans) # The power transmitting capacity and velocity ratio is low.

#They have large dimension, occupy more space and are noisy.

# Belts are placed horizontally and not vertically.

13.6) Flat-belt drives are not popular. Why?

Ans) Because of lot of disadvantages, Flat belt drive is not popular.

13.7) What are the applications of flat-belt drive?

Ans) It is used in belt conveyors, baking machinery, brick and clay machinery, crushers, saw mills, textile machinery, line shafts and bucket elevation.

13.8) What are the advantages of V-belts over flat-belt drives?

Ans) # V-belts have short centre distance that results in compact construction.

# Permit high speed- reduction even up to seven to one.

# The drive is positive because the slip is negligible due to wedge action.



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# V- belts can operate in any position, even when the belt is vertical.

13.9) What are the disadvantages of V-belt over flat-belts?

Ans) # The ratio of cross sectional height to the pulley diameter is large.

# The efficiency of V-belts is lower than that of the flat belts.

# The creep is also higher.

# The construction is complicated and costlier.

13.10) What are the applications of V-belt drive?

Ans) They are used as prime movers in compressors, pumps, fans, blowers and machine tools and they are also used in automobile to drive accessories on petrol or diesel engines.

13.11) Where do you use round belts?

Ans) They are used in dishwasher drives, sewing machines, vacuum cleaners and light textile machinery.

13.12) What are the advantages of round belts?

Ans) # Round belts can operate satisfactorily over pulley in several different planes. They are suitable for 90` twist, reverse bends or serpentine drive.

# They can be stretched over the pulley and snapped into the groove very easily. This makes the assembly and replacement simple.

13.13) What are the disadvantages of Round Belt?

Ans) The Round Belt are limited to low power distribution .Due to this it is limited to light duties. Used in dishwasher drives, sewing machines, vacuum cleaner.

13.14) What are the desirable properties of belt material?

Ans) The belt material should have high coefficient of friction ,high tensile strength ,high flexibility.

13.15) What are the materials by which flat belt are made?

Ans) Flat belt are made of leather ,canvas rubber or rubberized fabric and synthetic material.



Machine Design


13.16) What are the advantages of leather belt over fabric rubber belt?

Ans) The leather belt has high coefficient of fraction ,consequently high power transmitting capacity over fabric rubber belt.

13.17) What is the advantage of fabric rubber belts?

Ans) The fabric rubber belt has high load carrying capacity also long service life.

13.18) What are the disadvantages of fabric rubber belts?

Ans) The disadvantages of fabric rubber belts are ,they cannot operate on small diameter pulley ,also they are subjected to destruction in an environment of mineral oil ,gasoline alkalis.

13.19) How are the ends of flat belt are joined?

Ans) The ends of flat belt are joined by various joint such as cemented joint ,Laced joint ,joint with metal fasteners.

13.20) What is mean by ply of belt?

Ans) The ply is specific term used to specify thickness of belt that represent number of layer .

e.g. single ply ,Double ply.

13.21) What do you understand by single ply and double ply belts?

Ans) Single ply represent only one layer in belt, double ply belt is belt having two number of layer or plies.

13.22) What are the three basic parts of the cross section of V belt?

Ans) The basic parts are

Pitch width (WP):- it is the width of the belt at the pitch zone.

Nominal height (T): it is the height of the trapezium outline on the cross section.

Angle of belt (A):- it is included angle obtained by extending the sides of the belt.

13.23) Distinguish between open and cross belt drive



Machine Design


Ans) In open belt drive, both driving and driven pulleys rotate in same direction.

In crossed belt drive, driving and driven rotate in opposite direction.

In cross belt angle of lap is more hence power transmitting capacity is more.

13.24) What is optimum belt velocity for maximum power transmission?

Ans) The optimum velocity is: V=(P/3M)^0.5

P= initial tension

M= mass per unit length of belt

13.25) What is the effect of centrifugal tension on power transmitted by a belt drive?

Ans) The centrifugal force due to belts own weight tends to lift the belt from the surface of pulley, hence it decrease power transmission.

13.26) State the law of belting?

Ans) The law of belting states that the center line of belt as it approaches the pulley must lie in plane perpendicular to axis of that pulley or must lie in parallel to plane of pulley ,otherwise the belt will run of the pulley.

13.27) What condition should be followed while flat belt drive is installed?

Ans) The selection of belt is based on the power is to be transmitted ,the kind of loading, the center distance between pulley and pulley center.

13.28) In open belt drive ,which side of belt should tight &why?

Ans) In open belt drive the lower side of belt should tight to hold the grip on pulley ,the upper side of belt will rest on pulley by its own weight.

13.29) What data is read for selecting a flat belt from manufacturer’s catalogue?

Ans) Power to be transmitted

The input and output speed

Centre distance

Type of load

13.30) What is load correction factor for flat belt?



Machine Design


Ans) Load correction factor is fraction taken into account for loss or gain of arc of contact.

13.31) What is arc of contact factor for flat belt?

Ans) When the arc of contact is less than 180’, there will be additional tension in the belt, to account this factor is used called arc of contact factor.

13.32) What is belt rating?

Ans) Belt rating is defined as the power transmitting capacity of the belt per MM width per ply at 180 degree arc of contact.

13.33) State the different types of pulleys used in belt drives?

Ans) Flat pulley, v pulley, u pulley and multi grooved pulleys as per the requirement.

13.34) What are the materials by which pulleys of flat belts are made?

Ans) Cast iron and Mild steel.

13.35) What is crowning of belt pulley?

Ans) The thickness of the rim is slightly increased in the centre to give it a convex or conical shape. This is called as ‘crown’ of the pulley. Crown is provided because

I. The crown on the pulley helps to hold the belt on the pulley in running condition.

II. The crown on the pulley prevents the belt from running off the pulley.

III. The crown on the pulley brings the belt to equilibrium position near the mid-plane of the pulley.

13.36) Why is the cross section of the pulley arm elliptical? Why is the major axis of

Cross section in the plane of rotation?

Ans) Elliptical cross-section reduces the aerodynamic loses during the rotation of the pulley. Hence the cross-section is kept elliptical. It is observed that keeping the minor axis in the plane of rotation increases the cross-section area and hence it is economical to to keep the major axis in the plane of rotation.

13.37) What is the basis on which the minimum diameter of the pulley is selected?



Machine Design


Ans) The minimum diameter of the pulley depends upon the following factors:

I. The number of plies in the belt.

II. The belt speed.

13.38) What are the loses in belt drives?

Ans) The power loses in the belt drive are as follows:

I. Power loss due to belt creep on the pulley.

II. Power loss due to internal friction between the particles of the belt in alternate bending and unbending of the pulley.

III. Power loss due to aerodynamic resistance to the motion of the pulley.

IV. Power loss due to friction in bearings of pulley.

13.39) What is creep in belts?

Ans) Creep is the relative motion of the belt as it passes over the pulley. Whilemoving the belt passes from a region of high tension to low tension which shortens the belt and it creeps along the surface of pulley.

13.40) What is pitch width of V-belt?

Ans) It is the width of the belt at pitch zone.

13.41) What is nominal height of V-belt?

Ans) It is the height of the trapezium outlined on the cross-section of the belt.

13.42) What is pitch length of V-belt?

Ans) It is the length of pitch line of belt. This is the circumferential length of the belt at pitch width.

13.43) What is the standard value of belt angle for V-belt?

Ans) 40 degrees.

13.44) How will you classify the cross-section of V-belt?



Machine Design


Ans) The V-belt is classified in six categories depending on the cross-section. They are Z,A,B,C,D & E. they determine the power that can be transmitted by the belt.

13.45) How will you designate V-belt?

Ans) V-belts are designated by the symbol of cross-section followed by nominal pitch length along with symbol Lp

13.46) What is B 4430 Lp designation of V-belt?

Ans) B 4430 Lp denotes V-belt of cross-section B and with pitch length 4430 mm.

13.47) What is the standard value for the groove angle of V-belt pulley?

Ans) 34-38 degrees.

13.48) Name the two factors that decide the cross-section of V-belt?

Ans) The cross-section of V-belts depends on

Power to be transmitted.

Speed of the faster shaft.

13.49) How will you find out the number of V-belts required for a given application?

Ans) Number of belts

= ( P × Fa ) ÷ ( Pr × Fc × Fd )

Where, P = drive power to be transmitted (KW)

Fa = correction factor for industrial service.

Pr = power rating of single v-belt.

Fc = correction factor for belt length.

Fd = correction factor for arc of contact.

13.50) What is the correction factor for service in case of V-belt?

Ans) The correction factor for service in case of v belts is 1.0 to 1.8 depending upon the service and operational hours.

13.51) What data is required for selecting a V-belt from manufacturer’s catalogue?



Machine Design


Ans) The following data is required

Type of driving unit.

Type of driven machine.

Operational hours per day.

Power to be transmitted.

Input and output speeds.

Approximate centre distance depending upon the availability of space.

13.52) What is timing belt?

Ans) A timing belt is a ribbed v belt with evenly spaced teeths on the inside of the circumference. They can maintain the same angular position of the driven shaft as compared to the driving shaft.

13.53) In what way are timing belt superior to ordinary V-belt?

Ans) It has high strength to weight ratio, which allows for high pitch velocity.

The belt is thin and flexible, which permits the use of small diameter pulleys.

The length of the belt does not increase due to steel cords.

Timing belts are made with a care to give precise timing for example to an I.C.

engine for which a constant velocity is required so that the engine timing does

not fluctuate giving a smooth operation to it.

13.54) In what way timing belts are superior to ordinary V–belts?

Ans) Timing belts are made with a care to give precise timing for example to an I.C.

engine for which a constant velocity is required so that the engine timing does

not fluctuate giving a smooth operation to it.

13.55) What are the advantages of ribbed V–belts?

Ans) It is thin and flexible belt with no slip and variation in the output speed and no tensioning device is required like flat belt-drive, also no lubrication is required.

13.56) What are the disadvantages of ribbed V–belts?

Ans) It is costly, construction of sprocket is difficult and is more sensitive to misalignment than compared to V-belt.

13.57) What are the applications of ribbed V-belts?



Machine Design


Ans) It is used in automobiles for driving camshaft from engine crankshaft and it is also used in business machines, sewing machine, portable wood working machines, timing devices and power transmission units.

13.58) Why belts are provided with initial tension?

Ans) A loose belt mounted on the pulleys does not transmit any load due to which belts are provided with initial tension in order to transmit power.

13.59) Name the belt tensioning devices.

Ans) 1.Idler pulley mechanism 2. Rockwood belt drive or Pivoted motor mounting.

13.60)What is the function of an idler pulley in belt drives?

Ans) To increase the power transmitting capacity of the belt drive.

13.61)When do you prefer V-belts to a flat-belt?

Ans) When there is a need to have more internal friction and creep on the pulley.

13.62) Why V-belts are more powerful than flat-belts?

Ans) Because V-belts are thicker than flat-belts in cross-section and can sustain more tension and frictional properties are higher than that of flat belt transmitting more power and greater speed reductions say upto seven to one.

13.63)Why slip is less in V-belts compared with flat-belts?

Ans) Due to increased frictional force, the slip is less in V-belts compared with flat belts.

13.64) What are the three basic elements of chain drive?

Ans) 1. Driving sprocket 2. Chain 3. Driven sprocket

13.65) What are the advantages of chain drive?

Ans) It can be used for a wide range of centre distances, number of shafts can be driven in d same or opposite direction with a single driving sprocket, compact in construction and the chain does not require initial tension and has no slip.



Machine Design


13.66) What are the disadvantages of chain drive?

Ans) Greater wearing, not suitable for non-parallel shafts, unsuitable for precise motion due to polygonal effect, requires a housing, regular tensioning required, precise alignment always required and chain drives are noisy.

13.67) What are the applications of chain drive?

Ans) It is used in bicycle, motorcycles and automobile vehicle, also used in metal and wood working machinery to transmit power, chain drives are widely used in agricultural machinery, oil-well drilling rigs, building construction and material handling equipment.

13.68) What are the types of chain?

Ans) 1. Load lifting chains 2. Hauling chains 3. Power transmission chains.

13.69) What are the advantages of link chains?

Ans) Link chains are less noisy, can operate with small pulleys and drums, good flexibility in all directions and are simple in construction and easy to manufacture.

13.70) What are the disadvantages of link chains?

Ans) Link chains operate at low speed, susceptible to jerks and overload, heavy weight and failure is sudden and total.

13.71) What are the applications of link chains?

Ans) It is used in low capacity hoists, winches and hand operated cranes.

13.72) What are the applications of hauling chains?

Ans) These chains are only used for conveyor applications.

13.73) What are the five parts of roller chain?

Ans) 1. Pin 2. Bush 3. Roller 4. Inner link plate 5. Outer link plate.



Machine Design


13.74) What are the materials for the parts of roller chain?

Ans) The inner and outer plates are made up of medium carbon steel and pins, bushes are made up of carburizing alloy steels and sprockets are made up of cast iron.

13.75) Define the pitch of roller chain.

Ans) The pitch of the roller chain is defined as the linear distance between the axes of adjacent roller.

13.76) How will you designate roller chain?

Ans) It is designated as for example 08B or 16A i.e. A stands for American standards ANSI and letter B means British standard series, and the number indicates pitch of the chain.

13.77) What are simple and duplex roller chains?

Ans) A simple chains is one consisting of one element or part only; not combined or complex. A duplex roller chain is one having two sets of rollers linked together, used for heavy-duty applications.



Machine Design


Ch.1- Fundamentals of Machine Design

14.15) Define the pitch circle diameter of the sprocket in chain drive.

Ans) The pitch circle diameter of the sprocket is defined as the diameter of an imaginary circle that passes through the centers of link pins as the chain is wrapped on the sprocket.

14.16) What is the relationship between pitch circle diameter of the sprocket, pitch of the chain and number of teeth sprocket?

Ans) D=p/sin (180/z), where z is number of teeth on the sprocket.

14.17) How do you express the length of roller chain?

Ans) L=Ln×p, where L is length of chain and Ln is number of links in the chain.

14.18) What is the offset link of roller chain?

14.19) When the chain has odd number of links, an additional link, is called offset link.

14.20) What is the polygonal action in roller chain? How will you reduce it?

Ans) The chain passes around the sprocket as a series of chordal link which is similar to that of a non slipping belt wrapped around the a rotating polygon. It is reduced by increasing number of teeth on the sprocket.

14.21) What is the effect of increasing and decreasing the number of teeth on sprocket in chain drive?

Ans) If we increase the number of teeth on sprocket the effect of pull on chain is reduced and consequently it reduces the friction in chain joint, and if we decrease the condition is wise versa.

14.22) What is the reason for selecting even number of pitches or links for roller chain?

Ans) We select even number of links and pitches because the chain consists of inner and outer link-plates.

In chain drives, the sprocket has odd number of teeth and the chain has even number of links. Why?

In chain drives, the sprocket has odd number of teeth and the chain has even number of links because it facilitates uniform wear.



Machine Design


14.23) What are the types of failure in roller chain?

Ans) The roller chain fails because of four types of failure i.e. wear, fatigue, impact and galling.

14.24) Define breaking load of roller chain.

Ans) Breaking load is defined as the maximum tensile load, which if applied will result in chain failure.

14.25) What is service factor for roller chain?

Ans) The service factor takes into consideration the power to transmitted by the roller chain.

14.26) What is the multiple strand factor for roller chain?

Ans) It takes into consideration the variation of number of strands taken into consideration for the values of power ratings of the roller chain.

14.27) What is the tooth correction factor for roller chain?

14.28) What is the recommended centre distance in roller chain drive?

Ans) The center distance in chain drive should be approximately 30 to 50 pitches (30 to 50 times the pitch of the chain).

14.29) What are the materials for sprockets in roller chain drives?

Ans) Sprockets are made up of cast iron, stainless steel, plastic, steel, etc

14.30) What are the guidelines for selecting the number of teeth for sprocket in roller chain drive?

Ans) 1) Driven machine

2) Load classification

3) Source of power

4) KW to be transmitted

5) Diameter and RPM of driving shaft

6) Diameter and RPM of driven shaft

7) Center distance between shafts



Machine Design


14.31) What is idler sprocket in roller chain drive?

Ans) The idler sprocket is adjustable sprocket provided to adjust the tension in chains, it is installed on driven side.

14.32) What are the methods of chain tensioning?

Ans) a) Change the centre distance by moving the axis of one of the sprocket. b) Provide adjustable idler sprocket.

14.33) Why is horizontal chain drive preferred?

Ans) In case of vertical drive, due to sag, the tendency of chain is to leave the profile of the teeth at the lower side of the lower sprocket. Therefore, vertical arrangement requires more careful adjustment of chain tension in order to prevent the outward shaft of chain, due to this horizontal chain drive is preferred.

14.34) What are the methods of lubrication in roller chain drive?

Ans) a) Type-A (Manual or dip lubrication). b) Type-B (Bath or disk lubrication). c) Type-C (Oil stream lubrication).

14.35) What is silent chain?

Ans) The silent chain consists of a series of links formed from laminated steel plates. Each plates has two teeth with a space between them to accommodate the mating tooth of the sprocket.

14.36) What are the advantages of silent chain?

Ans) Operates more smoothly and almost noiselessly. Reliability is more due to laminated construction.

14.37) What are the disadvantages of silent chain?

Ans) More heavier, more difficult to manufacture and more expensive than roller chains.

14.38) What are the applications of silent chain?

Ans) Compare with roller chain, silent chain can be used for high speed applications.



Machine Design


14.39) Distinguish between gear and chain sprocket?

Ans) a) A gear meshes with another gear. A sprocket meshes with an intermediate link, which in turns meshes with another sprocket. b) The face width of gear is usually more with respect to its diameter. The sprockets are comparatively thin so as to fit between inner link plates of chain. c) The tooth of gears have involute profile, while circular arcs are used for the profile of sprocket teeth.

14.40) In motorcycles, chains are used and not belts. Why?

Ans) Due to following advantages of chains, they are used in motorcycles. a) Small overall dimensions than belt drives, resulting in compact unit. b) A chain does not slip and to that extent, chain drive is a positive drive. c) chain does not require initial tension. Therefore, the forces acting on the shafts are reduced. d) Chain are easy to replace.

15.01) What is a bearing?

Ans) A bearing is a mechanical element that permits relative motion between two parts, with minimum friction.

15.02) What are the functions of bearing?

Ans) a) Ensures free rotation of shaft or axle with minimum friction. b) Supports the shaft or axle and hold it in correct position. c) Takes up the forces that act on the shaft or the axle and transmits them to the frame or the foundation.

15.03) How bearings are classified?

Ans) a) Depending upon the direction of force that acts on them - Radial and Thrust bearing. b) Depending upon the type of friction - Sliding contact and Rolling contact bearing.

15.04) What is radial bearing?

Ans) A radial bearing supports load, which is perpendicular to the axis of the shaft.

15.05) What is a thrust bearing?



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Ans) A thrust bearing supports load, which acts along the axis of the shaft.

15.06) What is a sliding contact bearing?

Ans) In sliding contact bearing, the surface of the shafts sliding over the bush resulting in friction and wear.

15.07) What is a rolling contact bearing?

Ans) Rolling elements, such as balls or rollers, are introduced between the surfaces that are in relative motion. In this type of bearings, sliding friction is replaced by rolling friction.

15.08) What are the applications of sliding contact bearing?

Ans) a) crank shaft bearing in petrol and diesel engine; b) centrifugal pump; c) large size electric motor; d) steam and gas turbine; e) concrete mixer, rope conveyor and marine installation.

15.09) What are the applications of rolling contact bearing?

Ans) a) machine tool spindles; b) automobile front and rear axle; c) gear boxes; d) small size electric motor; e) rope sheave, crane hook and hoisting drum.

15.10) Why are ball and roller bearings called antifriction bearings?

Ans) In order to reduce friction, two surfaces are separated by a film of lubricating oil, because of which ball and roller bearings are called antifriction bearings

15.31) State any two advantages and two disadvantages of taper roller bearing?

Ans) Advantages:Taper roller bearing has more rigidity and can be easily assembled and dissembled due to seperable parts.

Disadvantages:Taper roller bearing cannot tolerate misalignment between the axes of shaft and the housing bore and taper roller bearings are costly.

15.32: Draw a neat labelled diagram of thrust ball bearing



Machine Design


15.33) State any two advantages of thrust ball bearings?

Ans) Thrust ball bearing carry thrust load in only one direction and cannot carry any radial load.The use of large no of balls result in high thrust load carrying capacity in smaller space.

15.34) What is the material of balls and races in rolling contact bearing?

Ans) The balls and races are made up of high-carbon chromium steel(SAE 52100 OR AISI 5210).

15.35) What is the material of cages in rolling contact ?

Ans) The cages are made from stampings of low carbon steel.

15.36) What is the material of rollers in antifriction bearings?

Ans) Antifriction bearings are made of white metal or bronze.

15.37) What is the heat treatment for the balls in rolling contact bearing?

Ans) The balls in the rolling contact bearrings are hardened to obtain surface minimum hardness of 58Rockwell C.

15.38) What is the heat treatment for the rollers in rolling contact bearing?

Ans) The rollers in the rolling contact bearrings are case carburized to obtain hardness of 58Rockwell C.

15.39) Suggest any two types of bearings to take up combined heavy axial and heavy radial loads?

Ans) Angular contact bearing and Deep groove contact bearing.

15.40) What is an antifriction bearings?

Ans) In sliding contact bearing sliding contact is replaced by rolling contact resulting in low co efficient of friction,therefore these bearings are called antifriction bearings.



Machine Design


15.41) Enumerate any two advantages and disadvantages of rolling contact bearings over sliding contact bearings?

Ans) In sliding contact bearing surface of shafts slides over the surface of bush resulting it to friction.In rolling friction bearings sliding frictions are replaced by rollin friction which much less than sliding friction.

In sliding contact bearin we have to use lubricating oil between bush and shaft to avoid friction’but in rolling shaft bearing we can avoid use of oil.

15.42) Define static load?

Ans) Static load is defined as the load acting on the bearing when the shaft is stationary.

15.43) What is the criterion for static load carrying capacity of ball bearings?

Ans) The criterion for static load carrying capacity is that the permissible static load depends upon the permissible magnitude of permenant deformation.

15.44) Define of ball static load bearing capacity bearing?

Ans) The static load bearing capacity bearing is defined as the static load which corresponds to a total permament deformation of balls and races ,at the most heavily stressed point of contact ,equal to 0.0001 of the ball diameter.

15.45) Name three factors on which static load carrying capacity depends?

Ans) The factors on which static load carrying capacity depends

The races are rigid and retain their circular shape.

The balls are equally spaced.

The balls in the upper half do not support any load.

15.46) What do you mean by the failure of rolling contact bearing

Ans) The failure of rolling contact bearing occurs due to breakage of parts like races or cage and the surface destruction and due to overloading.

15.47) What is the life of the individual ball bearing?

Ans) The life of individual ball bearing depends upon the hours of service at some given constant speed before it get fatigued.



Machine Design


15.48) Define rating life of bearing?

Ans) The rating life of a bearing is defined as the number of revolutions that 90% of the bearings will complete or exceed before the first evidence of fatigue crack.

15.49) What is the criterion for the dynamic load carrying capacity of ball bearing?

Ans) The criterion for the dynamic load carrying capacity is that in group of bearings 90% of bearings will reach or exceed the average life.

15.50) Define dynamic load carrying capacity of rolling contact bearings?

Ans) The dynamic load carrying capacity of rolling contact bearing is defined as the radial load in radial bearings that can be carried for minimum life of one million revolutions.

15.51) What is median or average life of rolling contact bearing?

Ans) The median or average life of rolling contact bearing is given by L50 or the life which 50% of the bearings will complete or exceed before fatigue failure.

15.52) What is equivalent dynamic load in rolling contact bearing?

Ans) The equivalent dynamic load in rolling contact bearing is defined as the constant radial load in radial bearings (or thrust load in thrust bearings), that if applied to bearing would give same life as that which the bearing will attain under actual condition of forces.

15.53) Write down the relationship between dynamic load carrying capacity, the equivalent dynamic load and bearing life.

Ans) The relationship between dynamic load carrying capacity, the equivalent dynamic load and bearing life is given by,

L10=(C/p)p

Where,

L10=rated bearing life (in million revolutions)

C=dynamic load capacity (N)

p=3(for ball bearings)

p=10/3(for roller bearings).

15.54) What is L10 life?



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Ans) L10 life is the rated life of a group of apparently identical ball bearings. It is defined as the number of revolutions that 90% of the bearings will complete or exceed before the first evidence of fatigue crack.

15.55) What is L50 life?

Ans) L50 life is defined as the median life or life which 50% of the bearings will complete or exceed before fatigue failure.

15.56) What is the relationship between L50 and L10 life?

Ans) The relationship between L50 and L10 life is given by

L50 = 5 L10.

15.57) Enumerate the steps for selection of rolling contact bearings for a particular application.

Ans) The basic steps for selection of rolling contact bearings for a particular application from manufacture’s catalogue consist of following steps:-

Calculate the radial and axial force acting on the bearing and determine the diameter of the shaft where the bearing is to be fixed.

Select the type of bearing for given application.

Determine the values of the radial (X) and thrust (Y) factors from the catalogue.

Calculate the equivalent dynamic load from the equation, P = XFt + YFa.

Make decision about the expected bearing life and express the life L10 in million revolutions.

Calculate the dynamic load capacity from the equation C = P (L10)1/3. Check whether the selected bearing of series 60 has the required dynamic capacity. If not, select the bearing of the next series and go back to Step (3) and continue.

15.58) State the data required for selection of rolling contact bearing.

Ans) The data required for selection of rolling contact bearing are Load, Alignment, Thrust, Max. Speed, Rigidity, and Noise.

15.59) What is the reliability of rolling contact bearing selected from manufacture’s catalogue?



Machine Design


Ans) Reliability of rolling contact bearings selected from manufacture’s catalogue is 0.9 or 90%.

15.60) State the types of failures in rolling contact bearings.

Ans) There are two basic types of failure-breakage of parts like races or cage and the surface destruction.

Failure by breakage of parts can be due to overload, misalignment in bearing or centrifugal force.

Failure by the surface destruction has following types:-

Abrasive Wear.

Corrosive wear.

Pitting and Scoring.

15.61) How are rolling contact bearings designated?

Ans) A rolling contact bearing is usually designated by three or four digits. The meaning of these is as follows:-

The last two digits indicate the bore diameter of bearing in “mm” (bore diameter divided by 5). For e.g. XX07 indicates a bearing of 35mm bore diameter.

The third digit from right indicates the series of bearing.

The fourth digit and sometimes fifth digit from right specifies the type of rolling contact bearings.

15.62) State any two advantages of using oil as lubricant compared with grease for rolling contact bearings.

Ans) Compared with grease, oil offers the following advantages:-

It is more effective in carrying frictional heat,

It feeds more easily into contact areas of the bearing under load: and

It is more effective in flushing out dirt, corrosion and foreign particles from the bearing.

15.63) State any two advantages of using grease as lubricant compared with oil for rolling contact bearings.

Ans) Compared with oil, grease offers the following advantages:-

Simple housing design,



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Less maintenance cost,

Better sealing against rust; and

Less possibility of leakage.

15.64) Enumerate any three advantages of needle roller bearings.

Ans) Needle bearings offer following advantages:-

They have small outer diameter. It is due to this reason that they are often used to replace sleeve bearings. This allows replacement with little or no changes in design.

They are compact and lightweight compared with other types of bearings.

They have large load carrying capacity compared with their size.

15.65) Where do we use needle roller bearings?

Ans) Needle roller bearings are ideally suited for application involving oscillatory motion such as piston pin bearings, rocker arms and universal joints. They are also suitable for continuous rotation where the load is variable or intermittent.

15.66) Why the coefficient of friction in needle roller bearings is higher than roller bearing?

Ans) Short rollers are accurately guided in their cage and races. Needles are not guided to that extent. This results in high friction in needle roller bearings.

15.67) What is the objective of preloading of rolling contact bearings?

Ans) The objective of preloading is to remove the internal clearance usually found in bearings.

15.68) Where do you use preloaded rolling contact bearings?

Ans) Preloaded rolling contact bearings are used in, Shafts and spindles in machine tools and precision equipments; Ball bearings, such as angular contact bearing; The interference fit between the outer race and housing.



Machine Design


Ch.1- Selection of Bearings

16.1) Define lubrication.

Ans) Lubrication is the science of reducing friction by application of a suitable substance called lubricant, between the rubbing surfaces of bodies having relative motion.

16.2) What are four objectives of lubrication?

Ans) The four objectives of lubrication are as follows:-

to reduce friction;

to reduce or prevent wear;

to carry away heat generated due to friction; and

to protect the journal and the bearing from corrosion

16.3) Name any two liquid lubricants?

Ans) Mineral and vegetable oil.

16.4) Name any one semi solid lubricant?

Ans) Grease.

16.5) Name any two solid lubricants?

Ans) Graphite and molybdenum disulphide.

16.6) What is thick film lubrication?

Ans) Thick film lubrication describes a condition of lubrication, where two surface of the bearing in relative motion are completely separated by a film of fluid.

16.7) What is a zero film bearing?

Ans) Zero film bearing is a bearing, that operates without any lubricant.

16.8) What is hydrodynamic lubrication?



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Ans) Hydrodynamic lubrication is define as a system of lubrication in which the load supporting fluid film is created by the shape and the relative motion of the sliding surfaces.

16.9) Enumerate the factor that form and maintain thick oil film in hydrodynamic journal bearing?

Ans) Temperature , viscosity ,pressure

16.10) What is hydrostatic lubrication?

Ans) Hydrostatic lubrication is define as a system of lubrication in which the load supporting fluid film, separating the two surfaces is created by an external source, like a pump, supplying sufficient fluid under pressure

16.11) Draw a sketch showing the pressure distribution around the periphery of a hydrodynamic journal bearing?

Ans)

16.12) What does journal bearing mean?

Ans) The portion of the shaft inside the bearing is called journal and hence the name journal bearing.

16.13) Why hydrodynamic journal bearing is called self acting bearing?

Ans) Since the pressure is created within the system due to rotation of the shaft, due to which this type of bearing is called as self acting bearing

16.14) Why hydrostatic bearing is called externally pressurized bearing?

Ans) Since the lubricant is supplied under pressure, this type of bearing is called as externally pressurized bearing.

16.15) Give two applications of hydrodynamic journal bearing?

Ans) Engines and centrifugal pump.

16.16) Give two applications of hydrostatic bearing?

Ans) Turbo generators, centrifuges and ball mills.



Machine Design


16.17) State any two advantages of hydrodynamic bearing over hydrostatic bearing?

Ans) Simple in construction and easy to maintain

16.18) State any two advantages of hydrostatic bearing over hydrodynamic bearing?

Ans) High load carrying capacity even at low speed and no starting friction.

16.19) Give two examples of thin film bearing?

Ans) Door hinges and machine tool slide.

16.20) What is footstep bearing?

Ans) The footstep bearing is a thrust bearing in which the end of the shaft is in contact with the bearing surface.

16.21) What is collar bearing?

Ans) The collar bearing is a thrust bearing in which a collar integral with the shaft is in contact with the bearing surface.

16.22) What is elastohydrodynamic lubrication?

Ans) When the fluid film pressure is high and the surface to be separated are not sufficiently rigid, there is a elastic deformation of the contacting surfaces. Since hydrodynamic film is developed due to elastic deflection of the part, this type of lubrication is called elastohydrodynamic lubrication.

16.23) What is bearing characteristic number as applied to the journal bearing?

Ans) A bearing characteristic number is a dimensionless group of parameters given by,

(xN/p). where,

x=absolute viscosity of the lubricant

N=speed of the journal

p=unit bearing pressure(load per unit of projected area of bearing)

16.24) What is bearing modulus as applied to the journal bearing?

Ans) The value of the bearing characteristic number corresponding to this minimum coefficient is called the bearing modulus.



Machine Design


16.25) What is meant by ‘square’ bearing?

Ans) When (l/d) ratio is equal to 1,the bearing is called square bearing

16.26) What are the advantages and disadvantages of long bearings over short bearings?

Ans) The long bearing has more load carrying capacity compared to short bearing. A short bearing, on other hand has greater side flow, which improves heat dissipation. Long bearing are more susceptible to metal to metal contact at the two edges, when the shaft is deflected under load.

16.27) What are the advantages and disadvantages of circumferential oil-groove bearing over cylindrical oil-groove bearing

Ans) The disadvantage of circumferential oil-groove bearing is that it has a lower load carrying capacity as compared to cylindrical oil-groove bearing.

16.28) Give two applications of circumferential oil-groove bearings

Ans) Circumferential oil groove bearings are used for the connecting rods and crank shaft for automotive engines.

16.29) Give two applications of cylindrical oil-groove bearings

Ans) Cylindrical oil groove bearing are used for gear boxes and high speed applications.

16.30) State any four desirable properties of a good bearing materials

Ans) 1)It should not stick or weld to the journal surface

2)It should have high compressive strenghth

3)It should have sufficient endurance strenghth

4)It should have property of conformability

16.31) Define conformability

Ans) The bearing material should have ability to yield and adopt its shape to that of the journal.This property is called conformability.



Machine Design


16.32) Define embeddability

Ans) The bearing material should be soft to allow the dust particles in lubricating oil to get embedded in the lining and avoid further trouble.This property is called embeddability.

16.33) What are the advantages and dis advantages of babbitt as bearing material?

Ans) The advantages of babbit as bearing material is that they have excellent conformability and embeddability.High cost and shortage of tin are there main limitations.They have poor fatigue strenghth.

16.34) Where do you use sintered metal bearings?

Ans) Sintered metal bearings are used in automobiles,textile machinery and machine tools.

16.35) State any four desirable properties of a good lubricant

Ans) 1)It should be available in wide range of viscosities

2)There should be little change in viscosity of the oil with change in temperature

3)The oil should be chemically stable with the bearing material and atmosphere

4)It should be commercially available at reasonable cost.

16.36) What is SAE?

Ans) The Society of Automotive Engineers(SAE) of USA as classified as lubricating oils by a number ,which is related to the viscosity of the oil in Saybolt Universal Seconds.

16.37) Define ‘additive’ for mineral oil

Ans) An additive is a substance added to mineral oil in order to improve a particular property of that oil. Mineral oil in which additive are mixed is called doped oil or base oil.

16.38) What is the purpose of additive?

Ans) An additive is a substance added to mineral oil in order to improve a particular property of that oil.

16.39) What is doped oil?



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Ans) Mineral oil in which additive are mixed is called doped oil or base oil

16.40) What are EP additives?Where do you use them?

Ans) Extreme pressure(EP)additives are used in applications such as gears, where the lubricant is subjected to extremely high local pressures,at which oiliness additives are ineffective.

16.41) What is 2T oil?What are its advantages?Where do you use 2T oil?

Ans) 2T oil is a popular variety of lubricating oil used on two-stroke engines in scooters,mopeds and motorcycles.Its advantages are:1)It is self mixing with petrol. 2)It prevents corrosion of engine components. 3)It controls deposits in the combustion chamber and reduces preignition.

16.42) What is grease?State its applications

Ans) Grease is a semisolid substance composed of mineral oil and soap. It is used in applications where clearance is large due to rough machining.Grease is normally recommended for inaccessible parts, where leakage of oil is objectionable.

16.43) State four important assumptions of Reynolds equation?

Ans) The lubricant obeys newtons law of viscosity

The lubricant is incompressible

The viscosity of lubricant is constant

The shaft and bearing are rigid

16.44) What is the ideal value of length to diameter ratio?

Ans) The ideal value off length to diameter ratio is 0.5 to 2

16.45) What is mean by square bearing?

Ans) when length to diameter ratio is 1, the bearing is known as square bearing

16.46) Define unit bearing pressure?

Ans) The unit bearing pressure is the load per unit of projected area of the bearing in running condition.



Machine Design


16.47) When length to diameter ratio is 1,what is optimum value of (h/c)for maximum load carrying capacity ?

Ans) The maximum load carrying capacity is 0.66 , when the length to diameter ratio is 1

16.48) When length to diameter ratio is 1,what is optimum value of (h/c) for minimum friction loss?

Ans) The optimum value of minimum friction loss is 0.60 ,when the length to diameter ratio is 1

16.49) Give two applications of circumferential oil groove bearing?

Ans) circumferential oil groove bearing are used for the connecting rods and crankshafts of automotive engines

16.50) Give two applications of cylindrical oil groove bearing?

Ans) Cylindrical oil groove bearing are used for gear boxes and high speed applications

16.51) Define eccentricity ratio in hydrodynamic journal bearing?

Ans) The eccentricity ratio is defined as the ratio if eccentricity to radial clearance

16.52) Define radial clearance?

Ans) The radial clearance should be small to provide the necessary velocity gradient.

16.53) Define minimum film thickness?

Ans) The surface finish of the journal and the bearing is governed by the value of film thickness.

16.54) What is bearing characteristic number number as applied to the journal bearing?

Ans) A bearing characteristic number is a dimensionless group of parameters by,bearing characteristic



Machine Design


16.55)What is bearing modulus as applied to the journal bearing?

Ans) The value of bearing characteristic number corresponding to this minimum coefficient is called the bearing modulus

16.56) What are the advantages and disadvantages of long over short bearing?

Ans) Long bearing has more load carrying capacity as compared to the short bearing.

Long bearing are more succepteble matal to metal contact at the two adjust when the shaft is deflected.

The longer the bearing more difficult it is to get sufficient oil flow.

16.57)What are the advantages and disadvantages of short bearing over long bearing?

Ans) Has greater side flow which improves heat dissipation.

Short bearing has lower load carrying capacity.

16.63) Explain the principle of oil bearing?

Ans) Oil ring in contact with shaft & dipping in bath below. Ring rotates along with shaft with lower speed & carries oil to shaft.

16.64) State any 4deasirable properties of good bearing material ?

Ans) It should not stick or weld to journal contact surface

it should have high compressive strength

it should have strength to avoid failure due to pitting

it should have reasonable coast & easily available in market

16.65) Give a list of material for solid contact bearing?

Ans) Babbit,bronze,cooper,lead,aluminium alloy

16.66) Define conformability?

Ans) Ability of bearing material to yield& adopt its shape to journal

16.67) Define embeddability?

Ans) Property of soft material to allow dirt particle to get embedded in lining

16.68) What is babbit?



Machine Design


Ans) Babbit is popular bearing material with different grade

16.69) Why babbit is called white metal?

Ans) Due to silvery appearance, it is called white metal

16.70) What are advantages & disadvantages of babbit as bearing material?

Ans) Advantages-

Excellent conformability, embeddbility

Corrosion resistance

Easily bonded to steel shell

Disadvantages-

High coast and shortage of tin

Poor fatigue strength

Strength decrease with increase in temperature

16.71) What are 2 verities of babbit?

Ans) lead based babbit

tin basedbabbit

16.72/73) Give typical composition of tin based babbit&Give typical composition of lead based babbit.?

Grade Sn Sb Pb Cu Zn

90 90 7 - 3 -

84 84 10 R 5.5 -

75 75 11 R 3 -

69 69 - - 1 30

60 60 11.5 R 3 -

20 20 15 R 1.5 -

10 10 14 R 0.75 -

6 6 15 R 1 -

5 5 15 R 0.5 -



Machine Design


16.74) Compare bronze with babbit as bearing material ?

Ans) Bronze is cheaper,stronger at high pressure ,got exellent casting & machining characteristics

Drawback is tendency to stick surface at high temprature

16.75) What are sinterd metal bearing? What are 2 varities of it?

Ans) It is made of compressed metal powder by sintering.types are

copper based sintered metal

iron based sintered metal

16.76) Compare iron based & copper based sinterd metal bearing

Ans) Cu based iron based

contain cu contain Fe

more corrosion ressistance less corrosion ressistance

bearing pressure is 60N/mm2 bearing pressure is 100N/mm2

16.77) Where do you use sinterd metal bearing ?

Ans) In automobiles,textileindusteries& machine tool

16.77-a) Give typical composition of copper lead bearings? Where do you use it?

Ans) -70% of copper & 30% of Pb

It is used in theme lining like white metal

It is used in heavy duty appln.At high temp.

16.78) what are commonly used non metalik bearing material ?

Ans) Graphite, teflon ,rubber etc.

16.79) State any 4deasirable properties ofgood lubricant?

Ans) Availability in wide range of viscosity

Small change in viscosity with change in temp.

Sufficient specific heat to carry away frictional heat

Available at reasonable cost



Machine Design


16.80) what is paraffinic oil?

Ans) It is composed of Straight & branched Chains of hydrocarbons

Gen Formula :CnH(2n+2)

16.81) what is naphthenic oil?

Ans) It is composed of saturated single ring, formation of hydrocarbon

General Formula: CnH2n

16.83) What is SAE ?

Ans) The Society of Automotive Engineers (SAE) of USA has classified lubricating oil by a number , which is related to viscosity of oil in saybolt universal seconds .

16.84) What is the approximate relationship between SAE number and viscosity of lubricating oil ?

Ans) SAE number corresponds to approximately one half of the viscosity of oil at 210 ◦F measured in terms of SUS(Saybolt Universal Minimum) .When the SAE number is more, it indicates more viscous oil.

16.85) State any four advantage of mineral oil over vegetable oil .

Ans) Compared to Vegetable oil ,mineral oil offers the following advantages :

○ Mineral oil are chemically inert.

○ They have a wide range of viscosities ,corresponding to different values of n

in the general formula.

○ They have little tendency to oxidize or form corrosive acids.

○ After periodic filtration ,they can be reused without any change of their properties.

○ At normal temperature , they are not liable to spontaneous ignition.

16.86) State any two advantage of vegetable oil over mineral oil.

Ans) Advantage of vegetable oil :

○These oils are referred to as fixed oils as they are non-volatile ,unless there is chemical decomposition. These property prevents them from being expelled from intimate contacts of solid surfaces by frictional heat.



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○They retain their viscosities at higher temperature much better than mineral oils.

16.87) Define ADDITIVE for mineral oil.

Ans) An additive is a substance added to mineral oil in order to improve a particular property of that oil.

16.88) What is the purpose of additive?

Ans) Purpose of additive is to improves particular property of oil.

16.89) What is doped oil ?

Ans) Mineral oil in which additive is added is called doped oil.

16.90) What is the purpose of oxidation inhibitor ?

Ans) Oxidation inhibitors are widely used in automotive lubricants .They compete with the base oil for oxygen and thus retard the formation of peroxides .They also decompose and break peroxide s and prevent further corrosion of bearing surfaces

16.91) What is detergent additive ?

Ans) Detergent additive function is similar to that of soap . The coating prevents the individual particles from combining ,thus preventing formation of aggregate .Since the particles are small ,they remain suspended in lubricating oil and do not cause wearing of bearing surfaces or clogging of oil passages .

16.92) What is VI improver ?

Ans) A viscosity index improver is a substance , which when added to mineral oils,increases viscosity at high temperatures . The popular VI improver is paratone which is a polymer of butylenes having the formula (C4H8)n where ‘n’ varies from 180 to 270 . Due ot large size of molecule ,the additive has extremely high viscosity .

16.93) What is pour point depressant ?

Ans) Pour Point is the lowest temperature at which the oil can flow . This is an important characteristic when the lubricant is used in refrigeration and air-conditioning equipment. When the temperature decreases below the pour point



Machine Design


, the wax is separated in the form of needle shaped crystals . Paraflow is used as pour point depressant .

16.94) What are anti-foam additives ?

Ans) Anti-foam additives are used in lubricants for aero-engines.In aircraft engines , a continuous formation of foam on the surface of the lubricating oil in the supply tank is often observed . Foaming is a serious problem at high altitudes . Silicon polymer is used as an anti-foam additive

16.95 What is oiliness ?

Ans) Oiliness is considered as an important property under the conditions of boundary lubrication. Oiliness is distinct from viscosity , and refers to friction –reducing capacity. Oiliness is a joint property of the lubricant and the metallic surfaces in contact.

16.96) What are EP additives ? Where do you use them ?

Ans) Extreme Pressure additives are used in applications , such as gears , where the lubricant is subjected to extremely high local pressures , at which oiliness additives are ineffective .

There are two types of EP additives ,active and mild :

○ Active additives include compounds of sulphur or chlorine .

○Mild additives include compounds of phosphorus and metallic soaps like lead naphthenate.

16.97) What is 2T oil ? What are its advantages ? Where do you use 2Toil ?

Ans) 2T oil is a popular variety of lubricating oil .

The advantage of 2T oil are as follows :

○ It is self-mixing with petrol.

○ It keeps the piston , piston rings , cylinder , plugs and exhaust port clean .

○ It prevents corrosion of engine components .

○ It controls deposits in the combustion chamber and reduces pre-ignition.

2T oil is used on two stroke engines in scooters , mopeds and motorcycles .

16.98) Why SAE 80 ,SAE 90 AND SAE 140 oils are used for the lubrication of gears?



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Ans) SAE 80 ,SAE 90 AND SAE 140 oils are used for the lubrication of gears for the following reasons :

○ They have excellent chemical stability even at high temperatures.

○ They can withstand extremely high local pressures in high – torque and low – speed conditions.

○ They protect gear assemblies against rust and corrosion .

16.99) What is grease ? State its applications ?

Ans) Grease is a semisolid substance , composed of mineral oil and soap .

Application of Grease is :

○ It is recommended for inaccessible parts , where leakage of oil is objectionable .

○ It is used where clearance is large due to rough machining .

16.100) Grease is thixotropic . What does it mean ?

Ans) Grease is thixotropic ,it means,It undergoes a change in apparent viscosity with the amount of shearing .

16.101) How do you classify grease ?

Ans) Greases are classified on the basis of the soap employed .

○ Lime base grease consists of calcium soap in mineral oils of grades SAE 10 to SAE 40 .

○ Soda – base grease is produced from sodium soap .

16.102) State the types of bearing failure .

Ans) The different types of bearing failures are :

○ Abrasive wear :

Abrasive wear on the surface of the bearing is a common type of bearing failure . It is in the form of scratches in the directions of motion often with embedded particles . Abrasive wear occur when the lubricating oil is contaminated with dust . foreign particles , rust or spatter .

○Wiping of bearing surface :

When the rotating journal touch the bearing , excessive rubbing occurs resulting in melting and smearing of the surface of the bearing. This type of failure is in form of surface of the bearing .



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○ Corrosion:

The corrosion of bearing surface is caused by the chemical attack of reactive agents that are present in the lubricating oil. These oxidation product corrode materials such as lead, copper, cadmium and zinc. Lead reacts rapidly with all oxidation agents .

○ Distortion:

Misalignment and incorrect type of fit are the major sources of difficulties in journal bearings. When the fit is too tight, bore distortion occurs. When foreign particles are trapped between the bearing and the housing during the assembly, local bore distortion occurs .



Machine Design


Ch.1- Design of Gears

17.1) State appplication of gear drives.

Ans) In automobiles,mechanical industries,automation.

17.2) State any four advantages of gear drive over other type of drives.

Ans) # It is a positive drive.

# Velocity ratio remains constant.

# It can transmit very large power.

# Efficiency is very high.

17.3) State any two disadvantages of gear drive over other type of drives.

Ans) # Maintenance cost is high.

# Require careful attention for lubrication and cleanliness.

17.4) In a gear speed reducer,why is the diameter of an output shaft greater than input shaft.

Ans) Diameter is inversely proportional to velocity so as to reduce speed of output shaft , diameter of output shaft is greater than input shaft.

17.5) In which gear drive is self locking possible?

Ans) Self locking is possible in Worm gears.

17.6) What is herringbone gear?

Ans) It is a special type of helical gear consisting of two helical gears with the opposite hand of helix.

17.7) What are the advantages of cycloidal teeth gears?

Ans) # Large contact area and good wear strength

# Phenomenon of Interference does not occur.

17.8) What are the advantages of involute teeth gears?



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Ans) # Pressure angle remain constant.

# Manufacturing cost is low.

17.9) State two important reasons for adopting involute curve for gear tooth profile.

Ans) # It satisfies the law of gearing.

# Module and pressure angle are completely interchangeable.

# Module and pressure angle can be machined from one single tool.

17.10) What are the advantages of 14.50 full-depth involute teeth gears?

Ans) # Basic rack system is composed of straight sides.

# System is satisfactory when the number of teeth on gears is large.

17.11) What are the advantages of 200full-depth involute teeth gears?

Ans) # It reduces the risk of undercutting.

# It reduces interference.

# It has greater length of contact.

17.12) What are the advantages of 200 stub involute teeth gears?

Ans) # Since the pinion is small,drive is more compact.

# Stub system transmit very high load.

# Lower production cost.

17.13) What is full-depth involute gear tooth system?

Ans) It is a system in which basic rack is composed of straight sides except for the fillet arcs.

17.14) What is thestub involute gear tooth system?

Ans) It is a system in which gears have shorter addendum and dedendum.

17.15 Why is the tangential component of gear tooth force called ‘useful’ component?

Ans) The tangential component is a useful load because it determines the magnitude of the torque and consequently the power which is transmitted.



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17.16) Why is the radialcomponent of gear tooth force called ‘separating’ component?

Ans) The radial component is a separating force towards the centre of the gear.

17.17) What is pitting?

Ans) Initial pitting or corrective pitting is a localised phenomenon i.e. pits at high spot and destructive pitting is fatigue failure at the surface of the gear due to load.

17.18) What is scoring?

Ans) It is stick slip phenomenon in which alternative welding and shearing take place

rapidly at higher spot.

17.19) What is the minimum number of teeth on spur gear? Why?

Ans) Minimum number of teeth on spur gear is 14.This is to avoid interference and undercutting.

17.20) Whatis a ‘hunting’ tooth?

Ans) The extra tooth which causes pinion to rotate before the same pair of teeth will

engage again.

17.21) Which type of gear is used for high velocity ratio? Ans) Helical gears are used for high velocity ratio.

17.22) What is mean by spur gear? Ans) In spur gear the teeth are cut parallel to the axis of shaft.

17.23) What conditions must be satisfied for a pair of gears to have a constant velocity ratio?

Ans) The distance between center of the two gear is constant and they have a common point.

17.24) State the fundamental law of gearing?

Ans) The fundamental law of gearing states that the common normal to the tooth profile at the point of contact should always pass through a fixed point called the pitch point in order to obtained constant velocity ratio.



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17.25) What are the conditions required for interchangeability in toothed gearing?

Ans) The condition which is required for interchangeability is pressure angle.

17.26) Which curves satisfy fundamental law of gearing? Ans) Involute and cycloidalcurves satisfy the fundamental law of gearing.

17.27) Define involute curve?

Ans) An involute is a curve trace by point on a line as the line rolls without slipping on a circle

17.28) Define cycloidal curve?

Ans) A cycloid is a curve traced by a point on the circumference of a generating circle as its rolls without slipping along the inside and outside of another circle.

17.29) What are the advantages of cycloidal teeth gears ?

Ans) 1 in case of cycloidal gears a convex flank on one tooth comes in contact with concave flank of mating tooth.this increases contact area and wear strength. 2 there is no interference in cycloidal gear.

17.30) What are the advantages of involute teeth gear ? Ans) 1) Involute gear results in reduction in manufacturing cost. 2) involute gear increases the maximum value in reverse direction.

17.31) State the two important reason for adopting involute curve for gear tooth profile? A)

17.32) What is pitch circle?

Ans) Pitch circle is a curve of intersection of the pitch surface of revolution and the plane of rotation.

17.33) What is base circle?

Ans) The base circle is an imaginary circle from which the involute curve of the tooth profile is generated.

17.34) What is addendum circle?



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Ans) The addendum is an imaginary circle that borders the top of gear teeth in the cross section.

17.35) What is dedendum circle?

Ans) The dedendum circle is an imaginary circle that borders the bottom of space between teeth in the cross section .

17.36) What is addendum?

Ans) The addendum is the radial distance between pitch and the addendum circle.

17.37) What is dedendum? Ans) The dedendum is the radial distance between pitch and the dedendum circle.

17.38) Why dedendum is more than addendum? Ans) The dedendum is more than addendum because of the clearance.

17.39) What is circular pitch?

Ans) The circular pitch is the distance measured along the pitch circle between two similar points on adjacent teeth.

17.40) What is diameter pitch? Ans) Diameter pitch is the ratio of the number of teeth to the pitch circle diameter.

17.41) What is a module ?

Ans) Module is defined as the ratio of pitch diameter to the number of teeth .

17.42) How do you specify the size of gear tooth ?

Ans) The module specifies the size of gear tooth . As the module increases size also increases

17.43) What is the relationship between number of teeth on penion & gear , module & centre distance ?

Ans) a= m*(p+g) /2

Where , a= centre distance, m= module , p= no. of teeth on penion gear ,g= no. of teeth on gear



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17.44) What is the pressure angle of gear tooth ?

Ans) The angle between common normal at the point of contact & with the common tangent to the two pitch circle is called as pressure angle

17.45) What is the effect of increasing or decreasing the pressure angle in gear design ?

Ans) Increasing the pressure angle makes tooth stronger , reduces inteference & undercutting , while reducing it causes in reduction in noise during operation

17.46) What are the advantage of 14.5 full depth involute gear teeth ?

Ans) Quietness of operation

17.47) What are the advantage of 20 full depth involute gear teeth ?

Ans) It reduces the risk of undercutting . tooth is stronger with a higher load carrying capacity . It has greater length of contact . It gives larger radius of curvature .

17.48) What are the advantage of 20 stub involute teeth gears ?

Ans) Since the pinion is small the drive becomes more compact . They are more stronger & cheap to produce

17.50) What is crowning of gear teeth ?

Ans) In crowning process the ends of the tooth are made slightly thinner by small amount. This is done to shift load toward the middle

17.51) What is full depth involute involute gear tooth system ?

Ans) This system consist of involute profile throughout the length of gear teeth

17.52) What is stub involute gear tooth system ?

Ans) This system consist of shorter addendum & dedendum for compact , strong & inteference free drive

17.53) What are the advantage & disadvantage of stub tooth ?

Ans) Advantage ) They have low interference & reduces undercutting , drive is more compact & strong

Disadvantage ) due to insufficient overlap vibration are likely to occur



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17.54) What is a gear ratio ?

Ans) The gear ratio or the velocity ratio is equal to the no. of teeth on on the last driven gear to the no of teeth on first driving gear

17.55) What is backlash in gear teeth ?

Ans) It is defined as the amount by which the width of tooth space exceeds the thickness of engaging tooth measured along the pitch circle

17.56) What factors influence backlash in gear tooth ?

Ans) Factors include error in profile , pitch , tooth thickness , helix angle & centre distance

17.57) What are the parameters required to required to specify spur gear ?

Ans) Power , speed , gear ratio are the parameters required to specify spur gear

17.58) Why tangential component of gear tooth force is called useful component ?

Ans) It is called useful because it determines the magnitude of torque to be transmitted

17.59) Why radial component of gear tooth force is called seperating component ?

Ans) It acts towards the centre of each mating gear & tend to separate them

17.60) How will you decide the direction of tangential & radial components of gear tooth force ?

Ans) The direction is decided by drawing FBD in which radial component acts towards

the centre of base circle , while tangential component acts in the direction

perpendicular to it.

17.61) What are the basic modes of gear tooth failures?

Ans) There are two basic modes of gear tooth failures:

1)Breakage of the tooth due to static and dynamic loads.

2)Surface destruction.



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17.62) What are types of gear tooth wear?

Ans) The principal types of gear tooth wear are as follows:

1)Abrasive wear

2)Corrosive wear

3)Initial Pitting

4)Destructive Pitting

5)Scoring

17.63) What is pitting?

Ans) Pitting is of two types viz Initial and destructive

1)Initial Pitting: The initaial pitting is a localized phenomenon, characterized by

Small pits at high spots.

2)Destructive Pitting: It is a surface fatigue failure, which occurs when the load on Gear tooth exceeds the surface endurance strength of the Material.

17.64) What is scoring?

Ans) Scoring is a stick slip phenomenon, in which alternate welding and shearing takes place rapidly at the high spots.

17.65) State the desirable properties of gear materials?

Ans) 1)The gear material should have sufficient strength to resist failure due to

breakage of the tooth.

2)The gear material should have sufficient surface endurance strength to avoid

failure due to destructive Pitting.

3)The material should have low coefficient of friction to avoid failure due to scoring.

4)The material should be made of Alooy steels rather than plain carbon steels to

avoid thermal distortion or warping during heat treatment process.

17.66) Name gear materials.

Ans) Gears are made of cast iron, steel, bronze and phenolic resins. Large size gears

are made of grey cast iron of grades FG 200, FG260 or FG350.



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17.67) What are non metallic gears? Where do you use them?

Ans) Non-metallic gears are those in which only pinion is made of non-metals such as

molded nylon, laminated phenolics like Bakelite or Celoron. Non-metallic gears

are used under following conditions:

1)The load is low and the pitch line velocity is low.

2)A long life is expected.

3)It is required to have quiet operation free from noise and vibrations.

4)The gears are likely to be affected by water and oil.

17.68) Where do you make gear integral with shaft?

Ans) If the diameter of dedendum circle exceeds the diameter of the shaft(Ds), at the point where the pinion is fitted, by less than(Ds/2), the pinion is made integral with the shaft.

17.69) What are the advantages of forged gears?

Ans) Forged gears offer following advantages:

1)In case of forgings, material utilization factor is (2/3), which is twice. This reduces the cost of the material.

2)Forged gear has lightweight construction which reduces inertia and centrifugal

forces.

3)The fibre lines of the forged gears are arranged in a predetermined way to suit

the direction of external force.

17.70) What is rimmed gear? What is its advantage?

Ans) A rimmed gear consists of a steel rim fitted on a central casting with hub, arms or webs. The rim is forged from alloy steel. Rim gears save costly high strength material.

17.71) What is interference in gears?

Ans) The tip of the tooth on mating gear, which is involute, interferes with non involute

portion of the addendum. This phenomenon of tooth profiles overlapping and

cutting into each other is called ‘interference’.



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17.72) How will you eliminate interference in gear teeth?

Ans) The following methods can eliminate the interference;

1)Increase the number of teeth on pinion.

2)Increase pressure angle.

3)Use long and short addendum gearing.

17.73) What do you understand by corrected gear?

Ans)17.74) What do you understand by uncorrected gear?

17.75 What is a minimum number of teeth on spur gear?Why?

Ans)

17.76) What is a hunting tooth?

Ans) It is an extra tooth on the larger of two gear wheels so that the total number of teeth will not be an integral multiple of the number on the smaller wheel.

17.77) What is the optimum value of face width in terms of module?

Ans) The optimum value of face width is (8m<b<12m). In the preliminary stages of gear design, the face width is assumed as ten times of module.

17.78) What stresses are induced in gear tooth?

Ans)

17.79) State the assumptions of Lewis equation?

Ans) The Lewis equation is based on the following assumptions:

1)The effect of the radial component which induces compressive stresses is

neglected.

2)It is assumed that the tangential component is uniformly distributed over the

Face width of the gear. This is possible when the gears are rigid and accurately

machined.

3)The effect of stress concentration is neglected.

4)It is assumed that at any time, only one pair of teeth is in contact and takes the



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total load

17.80) What is beam strength?

Ans) The beam strength is the maximum value of the tangential force that the tooth can transmit without bending failure.

17.81) What is Lewis form factor?

Ans) It gives relation between tangential forces & corresponding stress.

17.82) When pinion and gear are made of same material, which component is to be designed? Why?

Ans) Pinion. It is easy to manufacture & less cost with low FOS.

17.83) Why pinion is weaker than the gear made of same material?

Ans) If pinion is stronger than gear it will damage the gear. As cost of the gear is more than pinion.

17.84) When pinion and gear are made of different material, which component is to be designed? Why?

Ans)

17.85) Why permissible bending stress for gear tooth is taken as one third ultimate tensile strength?

Ans) Repeated or reversed stress cause bending stress in gear which is difficult to determine hence we considered it is 1/3 of ultimate tensile strength.

17.86) What is service factor for gear tooth load?

Ans) External load dynamics, reliability, and life and is used to calculate equivalent horsepower.

17.87) What is velocity factor for gear tooth load?

Ans) It is a factor used for determining the approximate dynamic load in the primary stages of gear design.



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17.88) What is dynamic load? What are its causes?

Ans) This load occurs when a pair of teeth is just coming into mesh. It causes noise and vibration.

17.89) What is wear strength of gear tooth?

Ans) Failure of gear tooth due to pitting occurs when contact stresses between two meshing teeth exceed the surface endurance strength of material.

17.90) What is ratio factor in wear strength of gear tooth?

Ans) Q= 2 Zg/ (Zg+Zp)

Where Zg= no. of teeth on gear

& Zp= no. of teeth on pinion

17.91) What is load stress factor in wear strength of gear tooth?

Ans)

17.92) What is internal and external gearing?

Ans) Internal- Two gears are meshing internally by means of proper engagement.

External- Two gears are meshing externally by means of proper engagement.

17.93) State two advantages of internal gear.

Ans) Compact construction and smooth, quiet working.

17.94) State two disadvantages of internal gear.

Ans) It is costly in manufacture and difficult in assembly.

17.95) In internal gear drive, the meshing external pinion alone is designed. Why?

Ans) By considering bending & wear conditions, Tooth of internal gear is stronger than that of the external pinion.

17.96) What are the advantages of planetary reduction gears as compared to ordinary gearboxes?



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Ans) Planetary gears over parallel axis gears include high power density, large reduction in a small volume, multiple kinematic combinations, pure torsion reactions and coaxial shafting.

17.97) Where do you use grease as gear lubricant?

Ans) In hand operated mechanism.

17.98) Where do you use oil as gear lubricant?

Ans) When operating speed is medium.

17.99) What are the methods of lubrication in gear drives?

Ans) Spray and splash method.



Machine Design


Ch.18- Design of Helical Gears

18.1) What is helical gear?

Ans) The gear whose teeth are cut in the form of a helix on the pitch cylinder called as helical gear.

18.2) Compare the contact between mating teeth of spur and helical gears ?

Ans) In spur gear contact occur along the entire face width of the tooth while in helical gear contact begins with point and gradually extends along the diagonal line across the tooth.

18.3) What are the advantages of helical gears over the spur gears ?

Ans) Load pick up is gradual, smooth engagement , quiet operation even at high speed.

18.4) Where do you use helical gears ?

Ans) These used in automobiles ,turbines ,and high speed application even up to 3000 m/min.

18.5) What is parallel helical gear ?

Ans) These mounted on parallel shaft and their teeth have opposite hand of helix.

18.6) What is crossed helical gear ?

Ans) These mounted on shaft with crossed axes. Their teeth may have same or opposite hand of the helix.

18.7) What is helix angle ?

Ans) It is defined as the angle between the axis of shaft and the centre line of the tooth taken on the pitch plane.

18.8) What is the normal range of helix angle ?

Ans) It is 200 – 450



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18.9) What hands of helix are used for parallel helical gears ?

Ans) Opposite hand of helix are used for parallel helical gears.

18.10) What is transverse circular pitch ?

Ans) The transverse pitch of a helical gear corresponds to the pitch of a spur gear with the same number of teeth and the same pitch diameter. It is measured in the plane rotation of the gear

18.11) What is normal circular pitch ?

Ans) The normal pitch of a helical gear is the pitch of the tool used to cut the teeth. It is measured in a plane perpendicular to the direction of the teeth.

18.12) What is transverse diametral pitch ?

Ans) Transverse diametral pitch (D.P) = 3.1416 (Transverse circular pitch (C.P.)

18.13) What is normal diametral pitch ?

Ans) Normal diametral pitch (D.P.) = 3.146 ( Normal circular pitch (C.P.)

18.14) What is transverse module ?

Ans) The module of tooth datum orthogonal to the center axis of gear is called transverse module.

18.15) What is normal module ?

Ans) Normal module is the value of the module in a normal plane of a helical gear or worm.

mn = mtcos β

18.16) What is axial pitch ?

Ans) It is the distance ,parallel to the axis ,between similar faces of adjacent teeth .

18.17) What is transverse pressure angle ?

Ans) Transverse pressure angle is the pressure angle in the plane of the helical gear tooth.



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18.18) What is normal pressure angle ?

Ans) Normal pressure angle is the pressure angle in the normal plane of a helical gear tooth

18.19) What is the relationship between transverse and normal pressure angles and helix angle ?

Ans) cos Ѱ =(tan αn)/(tan α)

18.20) What is virtual or formative helical gear ?

Ans) In the design of helical gears, an imaginary spur gear is considered in plane

A-A(normal to the tooth) with centre o having a pitch circle radius of r and module mn

It is called as formative helical gear.

18.21) What is virtual number of teeth in helical gear?

Ans) It is a number used in determining helical tooth strength.

18.22) What is the relationship between actual and virtual number of teeth and the helix angle?

Ans) virtual number of teeth = actual number of teeth /(cosine of the helix angle)3

18.23) Write down the expressions for three components of resultant tooth force in helical gears?

Ans) Fa = Ft tan ψ

Ft = Fn cos Øn cos ψ

Fr = Fn sin Øn

18.24) How will you decide the directions of three components of resultant tooth force in helical gears?

Ans) Following information is required to decide the direction of three components:

1.Which is the driving element? Which is the driven element?

2.Is the pinion rotating in clocwise or anticlockwise direction?

3.What is the hand of the helix? Is it right handed or left handed?



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18.25) What is the velocity factor for helical gears?

Ans) To account for the dynamic effect, a factor Cv known as Velocity factor or dynamic factor is considered.

18.26) What is the main disadvantage of a single helical gear? What is the remedy?

Ans) The main disadvantage of single helical gear is a axial thrust, it is prolem is overcome by herringbone and double helicle gears havig two sets of teeth that are set in a v shape.

18.27) How is the axial thrust in helical gears overcome?

Ans) Axial thrust in helical gears is vercome by herringbone and double helicle gears havig two sets of teeth that are set in a v shape.

18.28) What is the double helical gear?

Ans) These are the gears costructed by joining two identical helical gears and having groove between them.

18.29) What is herringbone helical gear?

Ans) These are the gears costructed by joining two identical helical gears, they don’t have any gears between two helical gears.

18.30) What is the difference between double and herringbone helical gears?

Ans) Double helical gears have a groove between two helical gears while the gears without groove are called as herringbone gears.

18.31) State two advantage of herringbone and double helical gears?

Ans) 1.The net axial force that acts on the bearings is zero.

2.Power transmitting capacity is high.

18.32) State two disadvantage of herringbone and double helical gears.

Ans) 1.They are expansive

2.The high degree of precision is required to locate herringbone and double



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18.33) Where do you use herringbone and double helical gear?

Ans) Herringbone and double helical gears are used in ships drives and turbines.

18.34) What is the range of helix angle in herringbone and double helical gears?

Ans) 20 degree to 45 degree.

18.35) What is a crossed helical gear?

Ans) Helical gears which are mounted on non-parallel shafts are called crossed helical gears.

18.36) What hands of helix are used for crossed helical gear?

Ans) Left-hand helix are used for crossed helical gear.

18.37) Compare the contact between mating teeth of parallel and crossed helical gears.

Ans) There is a line contact in case of paralleh helical gears where as there is a point contact in case of crossed helical gears.

18.38) Why crossed helical gears are not used for high power transmission?

Ans) They have very low load capacity, therefore they are not used in high power transmission.

18.39) State the applications of crossed helical gear.

Ans) Used in small internal combustion engines, feed mechanisms on machine tools.



Machine Design


Ch.19- Design of Worm Gears

Q1) What is a worm gear ?

Ans) Worm gear consist of worm which is threaded screw while worm wheel is a toothed gear.

Q2) Why do you use worm gear drive ?

Ans) Worm gear drives are used to transmit power between two non-intersecting shafts at right angles to each other.

Q3) What are the advantages of worm gear drives ?

Ans) The advantages of worm gear drives are as follows:

(i) The most important characteristic of worm gear drives is their high speed reduction. A speed reduction as high as 100 : 1 can be obtained with a single pair of worm gears.

(ii) The worm gear drives are compact with small overall dimensions, compared with equivalent spur or helical gear drives having same speed reduction.

(iii) The operation is smooth and silent.

(iv) Provision can be made for self locking operation, where the motion is transmitted from worm to worm wheels.

Q4) What are the draw backs of worm gear drives ?

Ans) The drawbacks of the worm gear drives are as follows:

(i) The efficiency is low compared with other types of gear drives.

(ii) The worm wheel, in general, is made of phosphor bronze, which increases the cost.

(iii) Considerable amount of heat is generated in worm gear drives, which is required to be dissipated by a lubricating oil to the housing walls and finally to the surroundings.

(iv) The power transmitting capacity is low. Worm gear drives are used for upto 100 kW of power transmission.

Q5) What kind of contact occurs between worm and worm wheel ?

Ans) The worm is a threaded screw, while the worm wheel is a toothed gear. The teeth on the worm wheel envelope the threads on the worm and give line contact between mating parts.



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Q6) Why are worm gear reduction units not preferred over other types of gearboxes for transmitting large powers ?

Ans) The efficiency is low as compared to other gear boxes. Also the power transmitting capacity is low.Heat is generated during power transmissionwhich is not desirable.

Q7) What are single-enveloping and double enveloping worm gear drives ?

Ans) Single-enveloping worm gear drive :

A single-enveloping worm gear set is one in which the gear wraps around or partially encloses the worm. This results in line contact between the threads of the worm and the teeth of the worm wheel.It is also called as ' cylindrical ' worm.

Double-enveloping worm :

A double-enveloping gear set is one in which the gear wraps around the worm and the worm also wraps around the gear. This results in area contact between the threads of the worm and the teeth of the worm wheel.It is also called as ' hourglass ' worm.

Q8) What are advantages of double-envelope worm gear drives over single worm gear drives ?

Ans) Double-enveloping worm gear drive has the following advantages :

(i)The contact pressure between the threads of the worm and the teeth of the worm wheel is low. This reduces wear.

(ii)The drive occupies less space for a given capacity. Double-enveloping worm gear drive needs only about two-thirds of the space and has about one-third of the weight compared to single-enveloping worm gear drive.

Q9) What are the 4 important parameters that are required to specify worm gear drive ?

Ans) A pair of worm gears is specified by four quantities in following manner :

z1/z2/q/m

where,

z1 = number of startys on the worm

z2 = number of teeth on the worm wheel

q = diametrical quotient

m = module (mm)



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Q10) What is diametrical quotient ?

Ans) The diametrical quotient is the ratio of the pitch circle diameter of the worm to the module.

Q11) What is axial pitch of the worm ?

Ans) The axial pitch of the worm is defined as the distance measured from a point on one thread to the corresponding point on the adjacent thread, measured along the axis of the worm.

Q12) What is the lead of the worm ?

Ans) The lead of the wormis defined as the distance that a point on the helical profile will move when the worm is rotated through one revolution. It is the thread advance in one turn.

l = px z1

Q13) What is the relationship between axial pitch of worm and module in worm gear drive ?

Ans) Axial pitch of worm is equal to pii multiple of module in worm gear drive.

Q14) What is the lead angle of the worm ?

Ans) The lead angle is defined as the angle between a tangent to the thread at the pitch diameter and a plane normal to the worm axis.

Q15) What is the relationship between number of starts on worm, diametrical quotient and lead angle of worm ?

Ans) Lead angle of worm is the ratio of number of starts on worm to the diametrical quotient of the worm.

Q16) What is the relationship between number of starts on worm, number of teeth on worm wheel and speed ratio of worm gear drive ?

Ans) Speed ratio is the ratio of number of teeth on worm wheel to the number of starts on worm.



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Q17) What is the relationship between number of teeth on worm wheel, diametrical quotient, module and centre distance ?

Ans) a = 1/2 m(q+z2)

Where,

a = centre distance.

m = module

q = diametrical quotient

z2 = number of teeth on worm wheel

Q18) What is the material for worm ? Why ?

Ans) The threads of the worm are subjected to fluctuating stresses and the number of stress cycles fairly large. The surface endurance strength is an important criterion in worm material. The core of worm should be kept ductile and tough to ensure maximum energy absorption. Therefore, worms are made of case hardened steel with a surface hardness of 60HRC and a case depth of 0.75 - 4.5 mm.

Q19) What is the material for worm wheel ? Why ?

Ans) The number of stress cycles is reduced by a factor equal to speed reduction. The final profile and finish of the worm wheel teeth is the result of plastic deformation. Therefore, the material should be soft and comfortable. Phosphor-bronze, with a surface hardness of 90-120BHN. Phosphor-bronze worm wheels are sand-cast, sand-cast and chilled, or centrifugally cast.

Q20) Why is the efficiency of worm gear drive low ?

Ans) Worm gear drives gives large speed reduction by obtaining large velocity ratio. So, the efficiency becomes low.



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Ch.22- Design of Thin Cylinder

22.1) What is thin cylinder?

Ans) When the ratio of the inner diameter of the cylinder to the wall thickness is than

15, it is called as thin cylinder.

22.2) Give practical examples of thin cylinder.

Ans) Practical examples of thin cylinder are boiler shells, pipes, tubes, storage

tanks, etc.

22.3) What are the types of stresses in thin cylinder?

Ans) Circumferential stress or tangential stress (σt) and longitudinal stress (σl) are the

types of stresses induced in thin cylinder.

22.4) ‘In case of thin cylinder subjected to internal pressure, the tendency to burst

lengthwise is twice as great as at tranverse section.’ Why?

Ans) In thin cylinder, the circumferential stress (σt) is twice the longitudinal stress (σl),

therefore, when the circumferential stress exceeds the yield strength, failure will

occur lengthwise. Thus the tendency to burst lengthwise is twice as great as at

tranverse section.

22.5) ‘In case of thin cylinder subjected to internal pressure, the tangential stress

should be the criterion for determining the cylinder wall thickness.’ Why?

Ans) Circumferential stress or tangential stress(σt) is twice the longitudinal stress (σl) in thin cylinder. Thus, in case of thin cylinder subjected to internal pressure, the tangential stress should be the criterion for determining the cylinder wall thickness.

22.6) What is thick cylinder?

Ans) When the ratio of the inner diameter of the cylinder to the wall thickness is less

than 15, it is called as thick cylinder.

22.7) Give practical examples of thick cylinder.

Ans) Hydraulic cylinders, high pressure pipes and gun barrels are the examples of



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thick cylinders.

22.8) What are the types of stresses in thick cylinder?

Ans) Tangential stress (σt) and radial stress (σr) are the stresses induced in thick

cylinder.

22.9) What is the criterion to distinguish between thin and thick cylinder?

Ans) The ratio of inner diameter to wall thickness can be used to distinguish between

thin and thick cylinder. If the ratio is more than 15, it’s a thin cylinder, if it’s less

than 15, it’s a thick cylinder.

20.10) What is the difference between stresses in thin and thick cylinders?

Ans) The difference between stresses in thin and thick cylinders is as follows:

In thin cylinder, the tangential stress (σt) is uniformly distributed over the cylinder

wall, while in thick cylinder, it has the highest magnitude at the inner surface of

the cylinder and gradually decreases towards the outer surface.

The radial stress (σr) is neglected in thin cylinders, while it is of significant

magnitude in case of thick cylinders.

22.11) When do you use Lame’s equation for cylinder wall thickness?

Ans) Lame’s equation is used to determine the wall thickness when the material of the

cylinder is brittle, such as cast iron or cast steel.

22.12) When do you use Clavarino’s equation for cylinder wall thickness?

Ans) Clavarino’s equation for cylinder wall thickness is used for cylinders with closed

ends and made of ductile materials such as mild steel or alloy steel.

22.13) When do you use Birnie’s equation for cylinder wall thickness?

Ans) Birnie’s equation for cylinder wall thickness is used for open cylinders made of

ductile materials.

22.14) What is autofrettage?



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Ans) Auto frettage is a process of pre-stressing the cylinder before using it in service. It is used in case of high pressure cylinders and gun barrels.

22.15) What are the methods of pre-stressing the cylinder?

Ans) The methods for pre-stressing the cylinder are as follows:

Using a compound cylinder consisting of two concentric cylinders with outer

cylinder shrunk onto the inner one.

The second method consist of overloading the cylinder before it is put into

service.

In the third method, a wire under tension is closely wound around the cylinder,

which results in residual compressive stresses.

22.16) What are the advantages of pre-stressed cylinder?

Ans) Pre-stressed cylinder have increased pressure capacity. Also the residual

compressive stresses close the cracks within the cylinder resulting in increased

endurance strength.

22.17) What is compound cylinder?

Ans) When two concentric cylinders are used with outer cylinder shrunk onto the inner

one, it is known as compound cylinder.

22.18) What types of stresses are induced in the jacket and inner tube of compound

cylinder?

Ans) Tangential stresses are induced in the jacket whereas, compressive stresses are

induced on the inner tube of the compound cylinder.

22.19) What is the function of gasket?

Ans) The function of the gasket is to maintain barrier against the transfer of fluid across the mating surfaces of a mechanical assembly.

22.20) Where do you use gaskets?

Ans) Gaskets are used in static joints such as cylinder blocks and cylinder head.



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Machine Design - Prof. Ibrahim Shaikh Answers To Questions 2015 Machine Design [email protected] Mob.: 9892128099 . 2